Part 12

The exterior surface of the hypostoma is sparingly covered by granules of larger size than in other Chiruri. The maculæ as seen in a cast are prominent near the posterior border, sunk in their centre and surrounded by a narrow distinct border line. In a horizontal section it as not been possible to detect any peculiar structure, only a dark border surrounding the interior clear surface.

Chirurus spinulosus NIECZKOWSKI.

Pl. III fig. 15.

We have had the interior surface of a hypostoma at our disposal from the lower Siluria, of Esthonia (Kuckers C^2) belonging to Dr. G. HOLM. The macula are well preserved, standing out black on the white surface, oblong, 1,5 millim. in greatest length (fig. 15). There are indications as of a great number of small lenses on these maculæ. Remarkable are the two elongated spots, almost 3 mm. in length, above these maculæ, of which already mention has been made under Ch. clavifrons.

=Chirurus= sp. indet.

Pl. III fig. 16.

The hypostoma of an undescribed species from Öland. The maculæ are lengthened, ellipsoid and smooth tubercles lying in a groove. The finely granulated surface of the hypostoma shows rare smooth spots interspersed, being on the inside smooth pits, from which again in casts of the hypostoma larger tubercles are moulded. Of the same nature are those that are visible on the nucleus of Chir. speciosus and others. There are still some undescribed Lower Silurian species, for instance one nearly related to Ch. conformis with tubercular maculæ. A large hypostoma from the Leptæna limestone of Dalecarlia, 33 millim. in length, has a longitudinal macula, 2 millim. in length, as seen on the inside of the fragment.

On pl. VI fig. 10 a little hypostoma is delineated that shows some resemblance with that of the Chirurus, but probably belongs to some other, unknown genus. It is Upper Silurian, found at Mulde in Fröjel, Gotland. It is of an elongated ovate shape, with the anterior border faintly arched, the anterior wings broad, truncate. A narrow elevated border surrounds the lateral and posterior margins. The somewhat vaulted surface is covered by fine granulations, and the macula, situated on equal distance from the anterior and posterior margins are ovate, smooth and directed obliquely inwards. There are two minute pointed processes on each side of the lateral borders and one on each side of the pointed posterior margin.

=Ctenopyge= LINSN.

=Ct. spectabilis= BR. (I, pl. XII, fig. 12 a).

A small lengthened, apparently smooth hypostoma with two globular tubercular maculæ near the posterior border. No mention made of them in the description of BRÖGGER. Cambrian. I am not, however, quite sure whether this really belongs to a Ctenopyge, as it rather more resembles the type of a Peltura as shown in Pelt. scarabæoides. As Ctenopyge is so nearly related to Sphærophthalmus it could be expected to see its hypostoma of the same type and the maculæ entirely wanting. The eyes of this genus have been described above at page 29.

=Cybele= LOVÉN.

=Cyb. bellatula= DALMAN.

Pl. IV fig. 2.

We give a new figure of the hypostoma to complete that of FR. SCHMIDT, pl. XIII fig. 9. The anterior wings are larger and obtuse, excavated below and the border rim is not so distinct all round as he has figured. There are two pair of oblique, lengthened grooves above each other. The opposite do not, however, join to form a coherent groove across the median field of the hypostoma, which is level between them. No maculæ. Nearer the anterior border close below the wings, there is a small roundish, dark spot. The surface of the hypostoma is granulated.

=Cyphaspis= ANG.

=Cyph. elegantula= ANG.

Pl. III figs. 22-25.

The hypostoma is elongated, anterior margin evenly arched, anterior wings triangular, lateral margins faintly curved as well as the posterior margin, at both sides of which there is one diminutive spine. The posterior wings are short forming a spiny process from the lateral margin. The surface of the hypostoma is smooth with a shallow transverse groove on the inferior moiety and two corresponding lateral impressions below it, one on each side. The elevated lateral borders are longitudinally striated by a few terrace lines. There are no maculæ visible. The eyes consist f short hexagonal prisms (figs. 22, 23) nearly resembling those of Proetus.

=Dalmanites= EMMRICH.

In this large genus the hypostoma has been figured in a great number of species. But it is only in the following that we, at least in the figures, if not in the descriptions, are able to detect the maculæ.

D. atavus BARR. Suppl. pl. 5 fig. 14.

D. Calypso J. HALL, vol. VII, pl. XI A. fig. 21 p. 66 »Postero-lateral pits, moderately strong and elongate». There are casts of the two well distinct maculæ.

D. caudatus BRÜNN.

a. FORBES and SALTER in British Organic remains, Dec. II pl. 1, fig. 3 give a good figure, showing the oblique pitlike maculæ. On page 2 is told that »a pair of lateral strong indentations indicate a second furrow above» (»the transverse furrow between the tip»).

b. SALTER, pl. 3, figs. 7, 8, bad figures, the description verbally the same as above. What ANGELIN pl. VIII, fig. 2 c gives as the hypostoma of »Ph. caudata» is in fact the hypostoma of a species of Lichas.

D. Mac Coyi BARR. Supl., pl. 13 f. 32. This magnificent hypostoma belongs to the same group as D. micrurus HALL as to which we may hesitate whether there not be a double pair of maculæ above each other near the posterior border. In this species, however, there is the transverse lower groove and above probably the two maculæ united by a groove so closely as to resemble the lower groove.

D. micrurus J. HALL, Pal. N. Y. III pl. 74 fig. 20. Shows, as it were, a double pair of maculæ, very like D. spinifer BARR.