510 DR G. S. BRADY ON 



posterior produced in the middle into a large, wide, and truncated beak ; dorsal margin 

 boldly arched, sloping steeply behind and more gradually in front; ventral almost straight, 

 rounded off at each end. Seen from above, the outline is elongated, subhexagonal, with 

 straight, parallel sides, which converge abruptly towards the extremities; anterior ex- 

 tremity obtuse, subtruncate, posterior produced, tapering and pointed at the apex. 

 Surface of the valves deeply excavated into a few (about twelve) polygonal, saucer-like 

 cavities, each with an elevated nodule in its centre. Length *43 mm. 



Habitat. — Levuka, between tide-marks. I have this species also from Princess 

 Charlotte Harbour in West Australia. 



This resembles so closely the well-known European species Cytherura cellulosa, 

 (Norman), that I at first thought the two to be identical. But C. cellulosa is more 

 angular in outline, has no distinct beak, and the surface excavations are much smaller 

 and more numerous than in C. scutellata. 



Genus Cytheropteron, G. 0. Sars. 



Cytheropteron coccoides, n. sp. (PL III. figs. 20, 21). 



Shell, seen from the side, elongated, subtrapezoidal, nearly thrice as long as high ; 

 height behind and in front equal. Extremities equal, depressed, produced and subangular 

 below the middle, the anterior angle somewhat rounded ; dorsal margin almost straight 

 in the middle, sloping with a steep curve at each end ; ventral slightly sinuated in front, 

 convex behind. Seen from above, oval, not quite twice as long as broad, widest in the 

 middle ; lateral margins evenly and boldly arcuate, extremities equal and almost rounded. 

 Surface smooth, a slightly produced flange running round the valves, except on the dorsal 

 margin. Length '46 mm. 



Habitat. — Mango Island, fringing reef. 



A very near ally of this species is a European one, C. humile, Brady and Norman, 

 but C. coccoides is more depressed fore and aft, is more tumid, more pointed in front 

 when seen dorsally, and has a distinctly papillose surface. 



Cytheropteron rude, n. sp. (PI. III. figs. 15-17). 



Shell, seen from the side, subrhomboidal, highest in front, height equal to more than 

 half the length. Anterior extremity very wide, obliquely rounded, the obliquity looking 

 upwards ; posterior tapered, produced in the middle to a subacute angle ; dorsal margin 

 high in front, sloping with a bold but irregular curve to the posterior extremity, ventral 

 margin irregularly sinuous, angulated behind. Seen from above, the outline is hexagonal, 

 widest in the middle, the width equal to nearly two-thirds of the length, lateral margins 

 for the middle third of their course straight and parallel, converging with a steep slope to 

 the acute anterior extremity, dipping at a right angle behind the middle, then sloping 

 sharply to the posterior extremity, which is acutely mucronate. End view very irregular, 

 wide at the base, which is produced laterally into rounded prominences, and is thrice 

 emarginate in the middle ; lateral margins very deeply sinuated, apex wide and emar- 



