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articular ridge of the tergum about three-fourths the length of the axial ridge, hardly shorter 
than the first. Scutal margin of the rostrum and tergal margin of the carina forming together a 
straight line. Rostrum and carina nearly of the same size, articulating with one another with 
from six to eight interlocking ridges. 
This characteristic species is the only species of Verruca collected by H. M.S. “Siboga’”’ 
which belongs to those which have the moveable valves almost parallel to the basis and ac- 
cordingly nearly perpendicular to the parietes (Pl. XII, fig. 1 and 2). It is the largest of the 
species collected by the Siboga, and at the same time one of the largest of the known species. 
Seen from the side of rostrum and carina it looks nearly symmetrical, seen from the side of 
the fixed scutum and tergum, in some specimens, the carinal side is more depressed than the 
rostral side, in other specimens this difference does not exist. The shells are dirty white; 
in some instances numerous specimens of very unequal size (and, no doubt, age) form groups, 
and are attached, partly to one another and partly so closely to one another, as to interfere 
with their normal growth and development. 
The moveable scutum (Pl. XII, fig. 3a) is relatively large; its shape is irregularly 
triangular with the apex strongly beaked. The irregularity of its shape is caused by the tergal 
margin having an excrescence formed by the broadest of the articular ridges, which does not 
extend to the basi-tergal angle. The basal margin of the valve is perfectly straight, the 
occludent margin curved. Of the three articular ridges, the axial ridge is narrow, and runs 
from the apex to the basi-tergal angle; the second ridge increases strongly in breadth from 
the apex to its inferior extremity, and it has the outer or tergal margin distinctly hollowed 
out. The so-called first articular ridge is very narrow and not quite half as long as the second. 
It can be seen best when the valves of a larger specimen are isolated and looked at from 
the side. On the under side the surface of the scutum is furnished with a very distinct rim 
along the occludent margin; from this rim, at a short distance from the apex, runs a trans- 
verse rim, separating the depression for the adductor muscle from a small triangular depression 
in which fits part of the scutal shoulder of the tergum. The tergal margin along this triangular 
portion is double, the interior margin representing the first articular ridge as indicated above. 
The moveable tergum (Pl. XII, fig. 34) is less than twice as large as the moveable 
scutum; it is broad and its shape is irregularly rhomboidal. Its scutal margin is characterised 
by a deep, rounded excavation, its basal margin is perfectly straight, one of its occludent margins 
(the longer) is feebly curved, the other being slightly hollowed out; a bluntly beaked apex 
is formed, where the two occludent margins meet. Externally three ridges are seen: a rather 
prominent axial ridge fitting with its basis against the axial ridge of the scutum; a middle 
(second) articular ridge, broad at the basis and much shorter than the axial ridge and the 
so-called first articular ridge, the free margin of which forms the shorter occludent margin of the 
valve. The broad extremity of this first or upper articular ridge is covered by the scutum and 
forms what might be called the scutal shoulder of the tergum fitting in the triangular depression 
at the under. side of the scutum. The under side of the moveable tergum (PI. XII, fig. 34) 
is flat and shows only two shallow grooves near the scutal margin. Along the two occludent 
margins the valve is bordered by distinct rims, which at the underside project over the surface. 
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