62 BULLETIN OF THE 



ASTROCERAS * gen. nov. 



Disk and arms covered with smooth, soft skin. Disk small ; its interbra- 

 chial outlines re-enteringly curved ; radial shields narrow and rather high, 

 running nearly to centre. Arms somewhat knotted by a contraction between 

 each pair of joints. Upper arm-plates divided in halves like high ribs, bearing 

 a jointed spine at their upper end. Side arm-plates, towards middle of arm> 

 having a long process to which are articulated the two spine-like tentacle- 

 scales. Teeth. A clump of grains on sides of mouth-angles, answering to 

 mouth-papilljB. Two vertical genital openings. 



Aslroceras stands next OpJiiocreas and Astroscliema. By its peculiar elon- 

 gated side arm-plates bearing spine-like, rough tentacle-scales, and the large 

 spines on the upper surface of the arm, it resembles the branching Euryale 

 asperum. 



Astroceras pergamena sp. nov. 



Plate XVIII. Fig:s. 478 -480. t 



Special Marks. — The smooth skin is translucent, allowing the underlying 

 parts to be seen. The upper ends of the halves of the upper arm-plates pro- 

 ject, and bear a stout spine. Tentacle-scales thick, rough ended, and nearly 

 equal in size. On the sides of the mouth-angle are elongated grains answering 

 to mouth-papillae. 



Description of an Individual (Station 235). — Diameter of disk 19 mm. 

 Length of arm about 100 mm. Width of arm at base 2 mm. ; height of same 

 2.5 mm. High up on the sides of the mouth-angles are elongated grains, irreg- 

 ularly arranged and answering to mouth-papillae, while at the apex is the low- 

 est tooth, flat and shaped like a wide spear-head. Mouth-shields very small, 

 triangular, with a rounded angle inward and outer edge straight. Side mouth- 

 shields very large and swollen, narrower without, meeting broadly within ; both 

 they and the mouth-shields are obscured by skin. Under arm-plates small, 

 and squarish, and occupying only a part of the length of a joint. Side arm- 

 plates nearly or quite meeting below, swollen and rounded, with a small pro- 

 jection to carry the two spine-like tentacle -scales ; further out, on the arm, 

 this projection is much elongated, forming an articulating process. Upper arm- 

 plates represented by two rib-like ridges, which do not meet above, but project 

 over the upper level of the arm, and bear a large, club-like, rough spine about 

 1.2 mm. long. Disk thin, and with deep constrictions in the interbrachial 

 spaces. The smooth translucent skin allows the long and narrow radial shields 

 to be seen ; they are pointed within where they do not meet, and are separated 

 their entire length; at their outer end they are elevated and carry a jointed 

 spine, similar to that of the arms. The first pair of arm-pores has no tentacle- 

 scales ; but those beyond have two, which are thick and club-shaped, with 



* ik<TT-fip, star ; K4pas, horn. 



