134 THE VOYAGE OF II. M.S. CHALLENGES. 



1 1. Shell not depressed. 



i, Movable scutum wilh three prominent longitudinal ridges, . . Verruca nexa, Darwin, 

 ii. Only one prominent longitudinal ridge is developed. 



(,,) Longitudinal ridge separated by a broad interspace from the 

 tergal margin, 

 1. Apex of the movable scutum projecting freely, . . Verruca sulcata, n. sp. 

 •-'. Apex i'f tlie movable scutum not projecting freely, . Verruca gibbosa, n. sp. 



(/<) Longitudinal ridge separated by a narrow interspace from the 

 tergal margin. 

 1. Immovable scutum divided into two triangular parts 



forming an angle together, ... . . . Verruca nitida, n. sp. 



•J.. Immovable scutum convex, ..... Verruca quadrangidaris, a. sp. 



(c) Longitudinal ridge close to the tergal margin. 



1. Apex of the carina very prominent and sharp, . . Venicca obliqua, n. sp. 



2. Apex of the carina not very prominent, . . . Verruca incerta, n. sp. 



Verruca gibbosa, n. sp. (PI. VI. figs. 17, 18 ; PL XI. figs. 5-9 ; PL XII. figs. 1-5). 



Shell white ; surface smooth, with very prominent growth-ridges and furrows between 

 the articulating ridges; walls almost perpendicular to the surface of attachment ; base 

 nearly triangular, not very narrow. Movable scutum rather large, with the upper articular 

 ridge hardly distinguishable, and a very prominent third articular ridge, which is separated 

 from the tergal margin by a rather broad interspace ; apex pointed, not projecting freely; 

 apex of the movable tergum almost pointed. Apex of the carina and rostrum recurved, 

 and projecting freely beyond the surface of the shell. Rostrum and immovable scutum 

 bulky. 



This is the largest and the most beautiful of the deep-sea species. It is represented by 

 four well-developed specimens. 



The surface of the shell is naked, no trace of a chitinous membrane being visible. The 

 growth-ridges can be distinctly made out on the operculum as well as on the other valves. 

 The surface of the rostrum and the carina, as well as that of the immovable scutum 

 is furnished with single deep furrows, which serve for the articulation of the valves. 



The movable scutum and tergum are by no means at right angles with the fixed pair : 

 they form one of the sides of a triangular pyramid, the two other sides of which are 

 formed by the immovable scutum and tergum. These latter are extremely steep. In 

 most specimens the movable scutum and tergum lie in a flat plane with part of the carina 

 and of the rostrum ; in one of the specimens (that figured PL VI. fig. 17) the rostrum is 

 convex beyond that plane. Of the sutures, that between the carina and rostrum is very 

 characteristically toothed ; that between the immovable scutum and immovable tergum is 

 not so obscure as in other species of the genus ; the immovable scutum shows a kind of 

 radius, which slightly projects over the immovable tergum. The carina also is furnished 



