7" 



tl )t - na is quite ilat in this specimen, thcn being hardly .1 tracé "I the longitudinal 



khich are distinct in the specimens ol Station r This difference, however, is not considered 



cient importanci t" separate from one another forms which quite correspond in 



other regards. Another difference is given b) the two rostral latera which meel in this specimen 



the whol( th «'t the rostral margins, .1 rounded space in the middle ol this margin 



onl) remaining uncovered l>\ calcareous matter. \ rostrum, however, could not be said to be 



.ent in tliis specimen eith 



N \lpellum um 11. sp. PI. VII, fig. 5 and 5a. 



Valves fourteen. Capitulum bulky, swollen, covered b) .1 thick chitinous membrane. 



Membranous interspaces between tin- valves. Umbo of the carina ai some distance from the 



valve angularly bent in consequence. Scutum and tergum imperfectlj calcified and 



divided into two parts by a prominent ridge, their occludent margin strongly convex. Si. les 



of tin- carina broad; upper latus pentagonal; infra-median latus elongated with the umbo near 



the base; carina] latus with tin- umbo near the base. Rostrum quite covered by membrane. 



This species is represented by three specimens. It is without doubt nearly related to 



ompressum^ mihi, collected by the "Challenger". lts bulkiness, the structure and imperfect 



calcification dl' scutum and tergum distinguish it at once from tin; "Challen^er" species. '1'he 



specimens were covered with mud; the outlines of the valves could only be made out alter 



the surface with a brush. 



The capitulum is relatively short, about one and a half times as long as broad, also 

 thick. swollen: its thickness is about IO mm. in a specimen the capitulum of which measures 

 17,5 X 27 mm. The thick chitinous membrane which covers the valves and the interspaces 

 between them, leaves uncovered the umbonal part of the scutum and the tergum. This chitinous 

 membrane is very characteristically pigmented on some of the valves, the scutum especialiv. 

 The chitinous interspace between the valves is particularly broad between the carina and the 

 other valvi 



The outline of the scutum is quadrangular, it is stromdv bowed in transverse direction. 

 i occludent margin is convex; where it reaches the tergum a recurved apex is formed which 

 overlaps a pan of the tergum. The calcified pan consists of an elongated occludent and a 

 short and narrow tergal segment. 



The tergum is rather quadrangular than triangular. lts occludent margin is stronglj 

 convex forming with the concave uppermost pari of the carina! margin a distinctly recurved 

 apex. The- scutal margin is nearly straight, the undermost part of the carinal margin which 

 forms the fourth margin of the quadrangle is also straight. The calcified part of the tergum 

 is V-shaped and is composed ol a broader occludent and a slightly narrower carinal segment. 



The carina lias the umbo at some distance trom the apex and the part above the 

 umbo forming an angle with the part underneath it. A rooi, slightly hollowed out longitudinally 

 and growing rather wide towards the base of the valve, can be distinguished from the sid< - 

 h are narrow at the base and ol considerable width in the uppermost part. 



7" 



