114 THE VOYAGE OF H.M.8. CHALLENGER. 



302 is indeed a full-grown one. As in many of the other cases in which I propose a new 

 species for a single specimen, it has only been done because it was an utter impossi- 

 bility to consider it as a specimen of one of the better established species. Future inves- 

 tigations, conducted upon a richer material, will alone be able to decide this question. 



Scalpellum ahi/ssicola, n. sp. (PI. VI. fig. 12). 



Surface of the valves covered by a very thin membrane, almost smooth. Valves 

 thirteen; they are thin and brittle. Umbo of the carina at the apex. Carina simply 

 but strongly bowed, with the roof fiat. Upper latus hexagonal, very large. Infra-median 

 latus oblong, quadrangular. 



This species is represented by a single specimen only. It is a small and rather 

 elongate species, in many respects resembling Scalpellum novce-zelandice, Scalpellum 

 Jiavum, &c. 



Capitulum elongate, surface unequal, a distinct gibbosity being observed near the 

 middle of the upper latus. The occludent margin is very slightly arched, the carinal 

 margin much more distinctly. Valves thirteen ; the chitinous membrane which covers 

 their surface is very thin. 



Scutum quadrilateral, elongate, large. Occludent margin slightly convex, tergal 

 margin a little hollowed out, apex — where the umbo is — slightly projecting over the 

 tergum. Lateral margin hollowed out at the superior extremity and slightly convex in 

 the inferior part. Basal margin slightly convex also. 



Tergum elongate, triangular. Occludent margin slightly convex, scutal margin 

 slightly hollowed out, carinal margin again convex. 



Carina elongate, with a flat roof regularly though not very strongly increasing in 

 width from the upper to the lower extremity. Sides well-developed, but more so in the 

 upper than in the lower half of the valve. The sides are about at right angles with the 

 roof. Umbo of the valve at the apex. 



Upper latus rather large. Tergal and carinal margins almost straight, basal margin 

 consisting of two parts, — a larger and slightly arched one separating it from the carinal 

 latus, and a smaller straight one against which the infra-median latus is placed. The 

 scutal margin follows the margin of the scutum, against which it is placed. 



Rostral latus, as the other latera of the lower whorl, rather high. Caused by the 

 shortness of the basal margin, the shape of the valve is nearly triangular. The rostral 

 margin is straight, and placed against the same margin of the valve of the other 

 side ; the scutal margin is slightly hollowed out, the lateral margin is again slightly 

 convex. 



Infra-median latus hour-glass-shaped, with the umbo about in the middle of the valve. 

 The basal margin is only a little broader than the upper margin. 



