176 



the basis. The rostrum is distinctly curved invvard 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 radii. (PI. 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 (PI. XV, fig. 20 and d) 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 ridgre can be distin^uished. 



The tergum (PI. XV, fig. 2a 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. Lab rum (PI. XV, fig. 4) has a shallow notch and four relatively strong 

 teeth disposed on each side. 



Pal pi (Ibld. 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 doublé 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. 



Mandible (PI. 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 doublé, 4 and 5 small, but 

 distinct. The inferior angle terminating in two extremely small points. 



Max il la (PI. 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 



48 



