ii7 



convex in the under part, where it forms a continuous curvature with the basal margin. It is 

 hollowed out in the lovver part where the apex of the upper latus borders upon it. 



The terg urn is triangular. The occludent margin is convex, the carinal margin is 

 slightly hollowed out above the middle at the place where the apex of the carina touches it. 

 The surface of this valve appears to be larger in the smaller (shown in fig. 2) than in the 

 larger specimens as represented in fig. 1. Apex distinctly recurved. 



The carina has a well-developed roof and narrow sides. The roof is not quite flat, 

 but laterally convex with narrow, rather flat borders. This valve is simply bowed, not very 

 strongly in the full-grown specimens, but much less so in the younger specimens, one of which 

 is represented in fig. 2. The carina of the latter is almost straight, making the convexity of 

 the occludent side of the capitulum much more prominent. 



The upper latus is the most characteristic of the valves: it is almost divided into 

 two nearly equal halves by a split or fissure reaching from the basal margin to near the umbo 

 of the valve : the same fissure has about the same relative length on both sides of the four 

 specimens at my disposal. The apex of the valve is truncatecl, the umbo is at the extremity 

 of a triangular portion which rises slightly above the surface of the valve. The carinal margin 

 of the upper latus is short, the basal margin hollowed out, being divided into two parts, the 

 longer of the two having a very conspicuous curvature. 



The rostral latus is quadrilateral with the lateral margin convex. The scutal margin 

 is slightly longer than the basal margin. 



The infra-median latus is wine-glass shaped and has the umbo very near to the base. 



The carinal latus is irregularly quadrangular. lts carinal margin is nearly straight, its 

 basal margin also straight. The lateral margin is convex and its upper margin is divided into two 

 parts, which meet together at an angle entering into the hollowed out basal margin of the upper 

 latus. Near its base the carinal margin has a little excrescence of nearly quadrangular form meeting 

 beneath the base of the carina with the same excrescence of the same valve on the other side. 



The peduncle is cylindrical. In all four specimens it is distinctly curved, more strongly, 

 however, in the full-grown specimens than in the smaller. Its base of attachment is prolonged 

 at one end towards the occludent side of the capitulum and is covered by a large number of 

 scales arranged in fairly regular rows. The number of these rows is greater in the larger than 

 in the smaller specimens; while they are at some distance from one another in the smaller 

 specimens, they nearly touch in the full-grown animal. In consequence of the peduncle being 

 bent it is not easy to count the number of the longitudinal rows; in the full-grown specimen 

 their number, however, is not less than 14 to 15. 



Si ze. The largest specimen had a capitulum of 9,2 mm. Its peduncle, if it could be 

 stretched quite straight, would measure about 7 mm. One of the smaller specimens had a total 

 length of 9,1 mm., its capitulum measuriiig 6,5 mm. 



The specimens are attached to small sterns or sticks of different nature. 



The study of the structure of the animal within the capitulum has yielded the 

 following results : 



Mouth slightly bullate; crest of labrum with a row of very minute bead-like teeth. 



117 



