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the basis. The rostrum is distinctly curved inward with its apical part. The radii are very 
broad, and their summits slightly hollowed out. The alae are broad also but have the upper 
margins somewhat convex. The shell is laterally compressed, and seems to have been attached 
to a narrow object with rounded surface. The basis is calcareous, and shows longitudinal canals 
running parallel to each other. The compartments have pores, which could not be discovered 
in the radi; (PL - XV, fig? 3): 
The shell is coloured beautifully red, with longitudinal and horizontal bands of a somewhat 
darker colour. The tips of the compartments and of the radii are of a lighter red. The radii 
are striated horizontally. 
The scutum (Pl. XV, fig. 26 and @) has the basal margin longer than the tergal 
margin; its lines of growth are rather broad and not very prominent. The external surface 
is not flat, but somewhat hollowed out in the middle; in consequence, the marginal parts — 
along the tergal and occludent margins — are slightly uplifted. Internally, the articular ridge is 
prominent and extends over two thirds of the length of the tergal margin. The cavity for 
the adductor muscle is distinctly indicated, the pit for the lateral depressor muscle very shallow. 
No. adductor ridge can be distinguished. 
The tergum (Pl. XV, fig. 2@ and c) has the articular ridge prominent, the articular 
furrow broad and rather deep. The spur is situated at some distance from the basi-scutal angle, 
and its extremity is bluntly pointed; the basal margin behind the spur is slightly hollowed 
out, the carinal margin is somewhat convex, the scutal margin straight. The crests for the 
depressores are strongly developed. The outer surface of this valve shows also a shallow 
excavation, the part which is somewhat hollowed out, being of triangular shape and lying between 
the apex and the middle part of the basal margin. 
The following description can be given of the structure of the animal’s body: 
Mouth. Labrum (Pl. XV, fig. 4) has a shallow notch and four relatively strong 
teeth disposed on each side. 
Palpi (Ibid. fig. 4*) are elongated, slightly broader towards the rounded extremity; 
the superior margin is almost straight, the inferior margin curved. Along the superior margin 
numerous hairs are disposed, which increase only slightly in length towards the free extremity 
of the palpus. Here they form a group with somewhat longer hairs disposed on the outer 
surface, as well as with the longest of those which form, on the outer surface also, a 
well-developed double row of hairs arranged along a line making a sharp angle with the 
inferior margin. The latter margin is occupied by a number of very delicate and short 
hairs, ciliae, arranged in small groups or brushes. The inner surface also is furnished with 
hairs, a row of the shortest being arranged parallel to, and at a short distance from, the 
superior margin. c 
Mandible (Pl. XV, fig. 5). Extremities of teeth 1 and 2 at a somewhat greater 
distance from one another than those of 2 and 3. Teeth 2 and 3 double, 4 and 5 small, but 
distinct. The inferior angle terminating in two extremely small points. 
Maxilla (Pl. XV, fig. 6 and 6*). Shape triangular, spine-bearing edge rather long. 
There are 2 upper spines, but the two at the inferior extremity are combined on one side with 
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