74 THE VoVAGE OF H.M.S. CHALLENGER. 



by Prof. .M. Sars, though nol very complete, is sufficient for its recognition. In general 

 appearance it much resembles Scalpellwm vulgare, but it may be distinguished at first 

 sighl by the smoothness "fits valves. 



The capitulum is robust, quadrangular; at the base it is a great deal thicker than near 



the upper extremity, in the middle of the lower whorl its thickness is increased still more 

 by a gibbous lateral excrescence. 



The scutum is rather small, slightly longer than broad; its apex distinctly projects 



over the tergum. 



The tergum is large, triangular, with the occludent margin convex and the apex 

 recurved. The carina! margin is almost straight, the scutal margin also. 



The carina is boat-shaped, with the umbo at one-fifth of the length of the valve from 

 the apex. The sides are well- developed, the roof in the lower part is almost flat. 



The upper lotus is of a pentagonal shape, the tergal and scutal margins being nearly 

 equal, as also the three other margins. 



The rostrum is well-developed, cuneiform, narrow at the apex, which projects 

 over the edge of the scutum, and considerably increasing in width towards the 

 base. 



The rostral latus is trapeziform, the basal and scutal margins being parallel to each 

 other, the first, however, being much shorter than the second. 



The infra-median latus is quadrangular, its height slightly surpasses its width. 

 The carinal latus has about the same area as the infra-median latus. The basal 

 margin is straight, the carinal margin slightly hollowed out in its superior, and convex 

 in its inferior portion. The lateral margin is also slightly hollowed out. The umbo 

 projects over the hind margin of the capitulum ; the umbones of the two carinal latera 

 almost touch each other under the middle of the carina. 



Length of the capitulum of the largest specimen 975 mm., breadth 5 - 5 mm. 

 The peduncle is short (3 mm.), cylindrical ; eight calcareous scales form together a 

 long-itndinal row, of which there are about nine. 



Mouth. — Labrum with the upper part highly bullate (PI. VII. fig. 12) and the 

 I lalpi elongate and very narrow, especially at the extremity, where they are furnished 

 with some large bristles. Mandibles (fig. 13) with three teeth, equidistant from 

 one another; the third tooth is sharply pointed. The lower edge of the mandible 

 is broad and truncated, both edges of the truncated part bearing three small teeth. 

 Maxillce (fig. 14) rather narrow, with the spinose edge straight; all the spines are of about 

 the same size, with the exception of the two uppermost ones, which are slightly greater. 

 Outer maxillce (PI. VIII. fig. 5) rounded; the inner margin is sparing!)' hairy, the 

 summit very hairy. The (so-called) olfactory orifices are placed at the extremity of a 

 tubular process. 



01' the cirri I wish to point out only that the first pair (PI. VII. fig. 12) has very 



