Part 9

Zapus trinotatus 385 Zapus trinotatus eureka A. B. Howell 389 Zapus trinotatus montanus Merriam 390 Zapus trinotatus orarius Preble 391 Zapus trinotatus trinotatus Rhoads 392

Zapus princeps 394 Zapus princeps cinereus Hall 399 Zapus princeps curtatus Hall 400 Zapus princeps idahoensis Davis 401 Zapus princeps kootenayensis Anderson 404 Zapus princeps luteus Miller 406 Zapus princeps minor Preble 407 Zapus princeps oregonus Preble 409 Zapus princeps pacificus Merriam 412 Zapus princeps princeps Allen 414 Zapus princeps saltator Allen 416 Zapus princeps utahensis Hall 418

Zapus hudsonius 420 Zapus hudsonius acadicus (Dawson) 432 Zapus hudsonius alascensis Merriam 435 Zapus hudsonius americanus (Barton) 436 Zapus hudsonius campestris Preble 441 Zapus hudsonius canadensis (Davies) 442 Zapus hudsonius hudsonius (Zimmerman) 443 Zapus hudsonius intermedius Krutzsch 447 Zapus hudsonius ladas Bangs 449 Zapus hudsonius pallidus Cockrum and Baker 450 Zapus hudsonius preblei Krutzsch 452 Zapus hudsonius tenellus Merriam 453

Genus =Zapus= Coues

Genotype.--Dipus hudsonius Zimmerman.

EXTERNAL CHARACTERS.--Muriform in general appearance; forelimbs small, short; hind limbs greatly developed; hind feet long and narrow; tail tapering, attenuate, subcylindrical; head long and mouse-shaped; eyes small and situated midway between nose and ear; external ear somewhat longer than surrounding hair and provided with antitragal flap which can cover external auditory meatus, and in company with tragus completely close opening; upper lip without median groove; internal cheek-pouches well developed and opening at corners of mouth; mystacial vibrissae conspicuous; supercilliary vibrissae few; genal tuft absent; teats normally eight and arranged in pairs (one pectoral, two abdominal, and one inguinal); anterior and posterior pairs frequently undeveloped; general pelage coarse; color of pelage varies somewhat in different species but always follows single basic pattern of broad dorsal band of some shade of brown or brownish-yellow darkened with brownish-black, sides of a lighter tone and slightly streaked with brownish-black, underparts snow-white, sometimes suffused with color of the sides and usually separated from color of sides by sharp line of clear brownish-yellow; backs of forefeet and hind feet grayish-white; tail distinctly bicolor, dark brown above and yellowish-white below; ears dark and narrowly edged with light color.

CRANIAL CHARACTERS.--Skull short in relation to width, deep relative to other dimensions, somewhat convex; delicate, papery, without strong angularity; braincase relatively unexpanded; antorbital foramen obliquely oval and transmits masseter muscle of great size; foramen in inferior ramus of zygomatic process of maxillary for passage of superior maxillary branch of trigeminal nerve small; zygomata not wide-spreading; underside of zygoma nearly horizontal, upper edge anteriorly rises prominently owing to extension of jugal upward along maxillary; jugal and lachrymal in contact; one ramus of zygomatic process of maxilla arises directly above other; rostrum thick basally and relatively attenuate distally; ends of nasals project noticeably beyond incisors; premaxillaries develop strong alveolar plate separating superior incisors for half their length; palatal bones shortened posteriorly, free edge often concave; incisive foramina long, broad, and separated by bulbose (except at posterior end) bony septum; mastoid bullae absent; auditory bullae short and transversely placed; postorbital process never present; parietals nearly square, sometimes emarginate in front; angle of mandible flattened and bent inward; coronoid process weak, acute, and slopes strongly upward.

DENTAL CHARACTERS.--Dental formula

I 1, C O, P 1, M 3 -- -- -- -- -- -- -- -- = 18; i 1 c o p o m 3

upper incisors short, compressed, curved backward, and strongly grooved; lower incisors slender, curved backward, and ungrooved; both upper and lower incisors deep orange or yellow; four upper cheek-teeth present; premolar small, single rooted and, sometimes, non-functional; upper molars tri-rooted, sub-hypsodont, and with occlusal surface non-cuspidate (flat); enamel pattern, much complicated, consisting of one main re-entrant fold lingually and four re-entrant folds labially; three lower molars, bi-rooted, sub-hypsodont, flat crowned, with two outer and four inner re-entrant folds.

POSTCRANIAL CHARACTERS.--Neck short and weak; atlas large; axis separate from atlas; remaining (5) cervical vertebrae also free; thoracic (12) and lumbar (7) vertebrae strongly built; posterior lumbars with enlarged neural and anteriorly directed transverse processes; sacral vertebrae (7) as in murids; caudal vertebrae variable in number (average 36); clavicle long, slender, uniformly curved, convex outwardly; scapula with supraspinous and infraspinous fossae of equal size; forelimbs short, approximately half as long as hind limbs; hind limbs elongate, slender; femur with third trochanter; tibia and fibula fused slightly distal to middle of former; five elongate, separate metatarsals (first and fifth subequal, shorter than others).

ARTIFICIAL KEY TO THE SPECIES OF THE GENUS ZAPUS

A. Baculum with tip spade-shaped and tip wider than 0.43 mm; underfur with medullary pattern rectangular, cuticular scales small; coronoid process of mandible long and slender, angle of divergence from condyle broad; angle of mandible turned in and wide; pterygoid fossae wide; skull broad in relation to length; premolars with crescentine fold on occlusal surface. Zapus trinotatus p. 385

A´. Baculum with tip lanceolate (not spade-shaped) and tip less than 0.43 mm wide; underfur with medullary pattern square or rectangular; but, if rectangular, cuticular scales large; coronoid process short and broad, angle of divergence from condyle narrow; angle of mandible turned inward and small to medium; pterygoid fossae usually narrow; skull not broad in relation to length; premolars without crescentine fold on occlusal surface.

B(A´). Baculum less than 5.1 mm in total length; guard hair averaging 115 micra in diameter; underfur with rectangular medullary pattern, cuticular scales large; skull small; incisive foramina shorter than 4.6 mm; condylobasal length averaging less than 20 mm; length of maxillary tooth-row averaging less than 3.7 mm; palatal breadth at M3 less than 4.2 mm. Zapus hudsonius p. 420

B´. Baculum more than 5.1 mm in total length; guard hair averaging more than 140 micra in diameter; underfur with square medullary pattern, cuticular scales moderately large; skull large; incisive foramina longer than 4.7 mm; condylobasal length more than 21 mm; maxillary tooth-row averaging more than 3.8 mm; palatal breadth at M3 more than 4.4 mm. Zapus princeps p. 394

SYSTEMATIC ACCOUNTS OF SPECIES AND SUBSPECIES

=Zapus trinotatus= Rhoads

(Synonymy under subspecies)

Range.--From southwestern British Columbia southward through western Washington and Oregon and in the humid coastal district of California almost to the Golden Gate (see fig. 45).

Characters of the species: External.--Size medium to large (total length 221 mm to 238 mm); tail longer than head and body (131 mm to 149 mm) and bicolored, brown above, white to yellowish-white below; hind feet long (31 mm to 34 mm), grayish-white above; back various hues and tones of ochraceous and tawny; sides paler than back; lateral line separating sides from ventral surface usually distinct and bright; ventral coloration white, usually with suffusion of ochraceous; ears usually dark, sometimes flecked, and usually narrowly edged with color of sides; guard hairs average 141 microns (133u to 155u) in diameter; underhair with medullary pigment in narrow, hollow rectangles; cuticular scales of underhair smaller and more numerous than in other species.

Baculum.--Size large (total length 6.7 mm to 7.4 mm); base broad (0.7 mm to 0.9 mm); tip broad (0.44 mm to 0.57 mm); spade-shaped in dorsal aspect and tilted upward, gradually tapering to thin-edged tip; shaft rounded, straight.

Skull.--Large, broad and deep in relation to length; pterygoid fossa broad; anterior ramus of zygomatic process of maxillary relatively narrow; nasofrontal juncture relatively broad; coronoid process of mandible elongate. Upper premolars relatively large (averaging .70 mm in length and .75 mm in width), usually functional, occlusal surface with labial re-entrant fold forming crescentine loop incompletely enclosing single central cusp; m3 relatively large, elongated; m1 elongated, broadly rounded anteriorly.

GEOGRAPHIC VARIATION

There are four subspecies currently recognized, all of which are confined to the Pacific coastal region of North America (See fig. 45). The features that vary geographically are external size, color of pelage (shade and tone of upper parts and tint of lower parts), and dimensions of certain cranial structures (zygomata, braincase, incisive foramina, palatal bridge, auditory bullae, and pterygoid fossae).

External size is smallest in the southernmost geographic race (Z. t. orarius) and largest in the northernmost geographic race (Z. t. trinotatus). This decrease in size from north to south is clinal and is in keeping with Bergman's Rule which postulates that within one species the smallest individuals occur in the warmer parts of its geographic range.

1. Z. t. eureka 3. Z. t. orarius 2. Z. t. montanus 4. Z. t. trinotatus]

Coloration of pelage is geographically variable. There is a gradual change in the color of the pelage from north to south. Animals obtained in the northern part of the geographic range of Z. trinotatus are generally darker dorsally (more tawny) with the ventral pelage usually pure white. Those individuals from the southern part of the geographic range of Z. trinotatus have the dorsal pelage lighter (more reddish and yellow-brown) and ventrally the pelage is usually heavily suffused with reddish-brown. The crania also vary geographically; they are largest in the northernmost part of the range of the species and smallest in the southernmost part.