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difference being that the surface of the rostrum in the latter species shows very prominent 
articular ridges, whilst these are absent, hardly visible or slightly prominent only in V. casszs. 
The articular ridges of the fixed tergum, moreover, which are well developed in V. créstaltina, 
show themselves only as feebly developed rims in V. casszs. 
4. Verruca grex na. sp. Pl. XI, figsj7— 132 2 i 1— 13: 
Shell not depressed, moveable valves nearly perpendicular to the surface of attachment, 
compartments broad, base also broad but very narrow. Moveable scutum and tergum each with 
four articular ridges. Rostrum, seen from the front, triangular and somewhat elevated, carina 
elongate and horizontally extended, articulating with the rostrum by means of one strong and 
three smaller teeth. Rostrum bending over to the side of the fixed scutum and tergum with a 
triangular part. Fixed scutum much larger than fixed tergum, the latter bending over to the 
side of the moveable valves with a triangular part. 
This interesting species was collected at several Stations. As a rule, numerous specimens 
are attached to the same spine of an Echinid (Pl. XI, fig. 7). The shell is white, its form very 
characteristic, which is due partly to its obliqueness, the moveable valves overhanging more or 
less towards the side of the carina, partly to the shape of carina and rostrum and to the way 
in which these compartments are articulated together (Pl. XI, fig. 8 and 9). 
The moveable scutum (Pl. XI, fig. ro) is relatively large, triangular, with the 
occludent margin very strongly curved, the basal margin nearly straight and the tergal margin 
with four shallow indentations in which fit the rounded extremities of the articular ridges of the 
moveable tergum. The apex is distinctly beaked; the part of the surface not occupied by the 
articular ridges shows very pronounced ridges of growth and is, moreover, longitudinally striped 
with shallow grooves. In this way a rather distinct fifth articular ridge is separated from the 
remaining part, close along the main or axial ridge. The latter ridge is the longest of all; it 
is strongly curved and runs from the apex to the basi-tergal angle, where its extremity forms 
a slightly projecting spur. The succeeding ridges are parallel to the main ridge, but each is 
shorter and slightly less curved than the preceding. : 
The moveable tergum (Pl. XI, fig. 11) is quadrilateral and nearly rhombiform. Its 
two occludent margins meet in a rather blunt angle; its basal margin is slightly convex and 
forms an obtuse angle with the extremity of the axial ridge. Its scutal margin shows indentations 
corresponding with the extremities of the articular ridges of the scutum. The main articular 
ridge is nearly straight, slightly curved only near the apex of the valve; it grows distinctly 
broader to the basi-scutal angle, where it forms a spur-like excrescence. The following articular 
ridges are all nearly straight, decreasing in length, so that the last one forms at the same 
time the shortest of the two occludent margins of the valve. The latter ridge is longitudinally 
furrowed and might in consequence be counted as two. The part of the valve between the 
axial ridge and the longest of the two occludent margins is triangular, shows distinct growth 
ridges and a few shallow grooves which run nearly parallel to the occludent margin. 
The rostrum is rather stout; a large triangular part of it is situated at the side of 
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