110 THE VOYAGE OF H.M.S. CHALLENGER. 



Scalpellum darmnii, n. sp. (PL V. figs. 1, 2; PL X. figs. 3-5). 



Surface and borders of the valves almost hidden under a thick villous membrane. 

 Valves fourteen. Carina simply bowed, massive, considerably increasing in width from 

 the upper to the lower part ; with the umbo at the apex, and with the roof convex and 

 gradually passing into the sides. Upper latus having the form of the sector of a circle 

 of about 50°. Peduncle rather long. Males four. 



This is the largest species of Scalpellum known. Only a single specimen of it was 

 dredged during the cruise of the Challenger. 



Capitulum consisting of thirteen valves, the carina being the only single one. Valves 

 covered by a brownish and very thick membrane, which, however, on the carina, 

 tergum, scutum, and upper lateral valve, diminishes in thickness from the lower to the 

 upper end, the latter in consequence being marked out by a fighter colour. 



Scutum broad, not quite twice as long as broad, convex, quadrilateral, with 

 the occludent margin the longest ; tergal margin slightly hollowed out, lateral margin 

 slightly convex. The umbo is at the uppermost point of the valve ; the lines of growth 

 run parallel with the basal and lateral margins. The apex does not project over the 

 tergum. 



Tergum large, having a greater area than the scutum ; fiat, oval, with the apex trun- 

 cated (having been broken off), and the basal angle pointed. The occludent margin is 

 straight, the carinal margin distinctly arched, the scutal margin being arched also, but 

 not so distinctly. Lines of growth not very distinct. 



Carina simply bowed, boat-shaped, with a rounded keel. Very broad near the lower 

 extremity, gradually growing narrower towards the upper end. Sides nearly as broad at 

 the lower end of the valve as close to the apex. Lines of growth oblique, meeting in 

 the median line. 



Upper latus triangular, large, with the apex pointed, the umbo being near the apex. 

 The side which is opposed to the apex, and which is composed of the carinal and the 

 basal margins, describes a beautiful curved line. 



Rostrum represented by an extremely small and very narrow valve between the 

 rostral angles of the rostral latera. Totally hidden under the chitinous membrane. 



Rostral latus trapeziform, with the scutal margin almost parallel to the basal margin ; 

 the rostral angle slightly projects beyond the scutum. 



Infra-median latus triangular, with nearly equal sides and a long basal margin. 



Carinal latus large, of an irregular shape, subtriangular, umbo projecting outwards, 

 the apex being distinctly beaked. A ledge starting from the apex describes a curve, and 

 separates a small depression from the basal margin of the upper latus. The carinal 

 margin is slightly convex, the triangular basal part of the carina being placed 



