IOI 



other species of the same group by the shape of the carina, by the rostrum and by the size 

 and form of the infra-median latus. 



25. Scalpellum discolor n. sp. PI. VIII, fig. 5. 



Valves thirteen covered by membrane. Tergum triangular, with the occludent margin 

 nearly straight and the carinal margin convex. Carina simply and not strongly bowed with the 

 umbo at the apex; roof flat bordered by ridges; sides hardly broader in the upper than in the 

 under part. Infra-median latus small, with the umbo at the apex and the lateral margins nearly 

 parallel. Umbo of the carinal latus at a short distance from the base, not projecting beyond 

 the line of the carina. Scales of the peduncle covering one another like the tiles of a roof. 



This species is represented by one specimen only. 



The capitulum is rather flat, broad, less than twice as long as broad. The carinal 

 and rostral sides are nearly equally convex; the occludent margin of the scutum forms an angle 

 with the nearly straight occludent margin of the tergum. Valves covered with a yellowish membrane 

 which is here and there distinctly pigmented with darker brown. The ridges of growth are very 

 distinct in most of the valves, the furrowing of the surface less distinct in most. 



The scutum is elongate with the umbo at the apex. The apex is produced, but can 

 hardly be said to project over the tergum. The occludent margin is feebly convex, the tergal 

 and basal margins are of about the same length, the lateral margin is strongly convex with a 

 small excavation near the upper extremity for the reception of the apex of the upper latus. 



The tergum is triangular with the occludent margin nearly straight. lts carinal margin 

 is convex and shows a tracé of an angular excrescence above the point where the apex of the 

 carina touches the carinal margin. About V. t ' d of the carinal margin extends beyond the apex 

 of the carina. 



The carina is simply and not strongly bowed, with the apex at the umbo. The flat 

 roof increases in breadth from the apex to the base and is bordered by distinct ridges. The 

 sides of the carina do not increase in breadth from the lower to the upper half of the valve. 



The upper latus has the umbo at a little distance from the apex, which forms a 

 pointed excrescence entering into the angle between the scutum and the tergum. The scutal 

 margin is strongly hollowed out. The shape of the valve is pentagonal. 



The rostral latus is quadrilateral with the scutal and basal margins of nearly 

 equal length. 



The infra-median latus is also quadrilateral. It has the umbo at the apex in the 

 corner where the four valves: the scutum and three latera meet. lts rostral-lateral margin is 

 hollowed out, its carinal-lateral margin nearly straight. 



The carinal latus has the umbo near the base at the carinal margin, which can 

 hardly be said to project beyond the line of the carina. 



The peduncle is short, truncated, conical. The scales cover one another like the tiles 

 ot a roof. They are not very numerous and arranged in 8 or 9 longitudinal rows. 



Size. The total length of the specimen is 18,6 mm., that of its capitulum 14,5 mm. 



