Part 18

Par. Tessini, var. Wahlenbergi ANGEL. Pl. I a, fig. 1 b.

Par. Tessini, var. oelandicus ANG. Tab. I a, fig. 2 b. ANGELIN'S figure of this hypostoma is incomplete in so far that he had not found the peculiar falciform horns on both sides of the posterior border. Pl. V, fig. 33.

Par. rugulosus CORDA has, according to BRÖGGER, Krækling, pl. II fig. 2 two long, straight callosities, probably corresponding to the maculæ in other Paradoxidæ.

CHR. BOECK gives in Mag. for Naturvidenskaberne Bd 8, 1828, in his paper on the Trilobites on the plate fig. 16 the hypostoma of a Bohemian species with well developed concave maculæ, probably a cast. He compares it with the Entom. bucephalus of WAHLENBERG, but says he cannot explain its nature.

The maculæ of P. oelandicus, pl. V, fig. 34, are tubercles, oblong, smooth, and have invariably an oblong scar along the centre, where probably once a thinner membrane, as in the cephalic eyes of Calymmene, contained the lenses.

=Peltura= M. EDW.

=Peltura scarabæoides= WAHLENB.

Pl. III fig. 42.

We have given a figure of the hypostoma, showing two large, elongated tubercular maculæ or rather resemblances of such, as they are covered with terrace lines as well as the rest of the surface. They have, however, the same position as real maculæ might have, but are directed in a line parallel with the longitudinal axis of the hypostoma. The cephalic eyes have been described above at page 29.

=Phacops= EMMRICH.

Maculæ figured of Phac. (Acaste) Downingiæ. SALTER Monogr. pl. 2 fig. 34 b, p. 25 »high up on each side a small tubercle».

Phac. rana HALL Pal. N. Y. vol. VII, pl. VIII A, fig. 18. Hypostoma with the large commalike maculæ high up.

Of the following species Ph. cephalotes and Ph. macrophthalmus belong to the genus Phacops proper, while Phac. quadrilineata, as well as Ph. Downingiæ are of a quite different generic type. The name Acaste proposed for them is not good as LEACH in 1817 named a Cirrhiped as Acasta.

=Ph. cephalotes= BARR.

Pl. V figs. 35, 36.

The hypostoma is elongate, almost triangular, tricuspidate at the posterior border, a little above this there is a crescent-shaped ridge, and still a little higher above this and the median horizontal line, the two macula, as diminutive tubercles. Seen with magnifying powers they are slightly oblong or reniform.

=Ph. macrophthalmus= BURM.

Pl. VI figs. 1-9.

The triangular hypostoma has a little below the median horizontal diameter two shallow grooves, and a little above the same diameter the extraordinary minute maculæ may with some care be observed, figs. 8, 9. They are visible as a small bare, smooth spot amongst the curious elevated and incoherent terrace lines of the surface. The exceedingly small size of these maculæ naturally does not allow any research of their structure. They are rather in this species and many of the congeneric to be regarded as small ocelli. In some specimens these spots are quite rudimentary and are reduced to the smallest area possible. The anterior wings are of a peculiar earlike shape, finely striate, enlarged and flat near the hypostoma and ending in a little hollow horn (figs. 6, 7). A little below it, the posterior wing emerges as a small angular knob. The aggregate cephalic eyes are more distinct.

As the vertical section learn us the regular ovate lenses consist generally of clear, crystalline calcareous spar and are on the surface covered by an extremely thin membrane, not a common one for all, but a separate cornea for each lens, which envelopes its superior moiety and continues down as a thickened appendix between the lens and the interstitial test (figs. 3-5). In the horizontal sections it surrounds the lenses as an annular wall. Around some lenses there is as if still another ring lay outside this, but more indistinct, probably only clearer portions of the test surrounding them. The cheeks close to the lenses are indistinctly perforated by longitudinal tubes.

=Phacops (Acaste) quadrilineata= ANGELIN.

Pl. V figs. 37, 38.

We have not succeeded in finding any well preserved hypostoma.

The lenses of the cephalic eyes resemble much those of the preceding species though more elongate and ovate. They are covered by a membrane which surrounds their upper moiety and between the lenses joins the interstitial test. In the horizontal section these membranes surround the lenses as an annular wall.

=Phaëtonides= BARR.

=Ph. Stokesi= MURCH.

Pl. VI fig. 11.

The hypostoma somewhat reminds of that of Calymmene, has projecting angles and a prominent knob below the straight anterior border. The two oblique and oblong macula are tubercular and placed near the lateral borders. This hypostoma is upon the whole much related to that of Phillipsia and Proetus.