ti4 THE VOYAGE OF II. M.S. CHALLENGER. 



i. Upper latus quadrant-shaped, with the arched side 



deeply notched, .... Scalpellum ornatum, Gray, sp. 



ii. Upper latus irregularly oval, . . Scalpellum vidgare, Leach. 



ji. 1'nibo of the carina at a small distance from the apex. 



i. Infra-median latus large, oblong-quadrangular, Srat/n'1/um sfrocmii, Sars. 



ii. Infra-median latus large, wine-glass-shaped, . Scalpellum carinatum, n. sp. 



iii. Infra-median latus small, triangular, . . Scalpellum recurcirodnim, 



n. sp. 

 B. Rostrum wanting or not distinct, ..... Scalpellum compressum, n. sp. 



('. Species with the carina simply bowed. 



a. With a sub-carina, ...... Scalpellum acutum, n. sp. 



B. Without a sub-carina. 

 (a) Rostrum present. 



u. Rostrum not covered laterally by the free edges of the 

 rostral latera. 

 i. Rostrum wedge-shaped. Carina short, . . Scalpellum brevecarinatum, 



n. sp. 

 ii. Rostrum elongate, narrow. Carina long, . , Scalpellum angustum, (!. 0. 



Sars. 

 iii. Rostrum wine-glass-shaped. Carina long, . Scalpellum parallelogram ma . 



n. sp. 

 iv. Rostrum protuberant, hook-shaped. Carina long, Scalpellum hamatum, G. (). 



Sara 

 8. Rostrum covered laterallj- by the free edges of the rostral 

 latera. 

 i. Rostrum large oval. 



(i) Valves separated by distinct chitinous inter- 

 vals, ..... Scalpellum album, n. sp. 



(ii) Valves not separated by chitinous intervals, . Scalpellum africanum, n. sp. 

 ii. Rostrum small, distinctly visible at the surface. 



(i) Surface of the valves with long hairs, . Scalpellum hirsutwm, n. sp. 



(ii) Surface of the valves smooth, or with short 

 hairs. 



1. Infra-median latus quadrangular, . Scalpellum nymphocola, n. sp. 



2. Infra-median latus triangular, . . Scalpellum nihrum, n. sp. 



3. Infra-median latus elongate, narrow, . Scalpellum corwuium, G. 0. 



Sars. 

 -1. Infra-median latus very small, . . Scalpellum striolatum, G. 0. 



Sars. 

 iii. Rostrum extremely narrow, hardly visible at the 

 surface, 

 (i) Terguni bluntly truncated, . . . Scalpellum truncatum, n. sp. 



(ii) Tergum triangular, not truncated, . . Scalpellum elongatum, n. sp. 



iv. Rostrum only visible after the chitinous membrane 

 has been taken away, 

 (i) Umbo of the carinal latus almost at the base of 



the valve, .... Scalpellum antarcticum, n. sp 



(ii) Umbo of the carinal latus at a distance from 

 the base. 

 1. Roof of the carina flat. 



