104 COLIECIIOirS PROM MELurasiA. 



in form, tie more UBual outline being represented by Reeve's fig. 

 47 h, which he wrongly ascribes to the West-Indian species. The 

 diflferenee in the angle of divarication of the ridges is at once seen 

 by comparing the two figures 47a and 47 h. 



43. Diplodonta subcrassa. (Plate VIL figs. 1, 1 1.) 



Shell roundly subquadrangular, only moderately inflated, thickish, 

 decidedly inequilateral, dirty white, not glossy. Anterior side 

 shorter than the posterior, somewhat pointed at the extremity ; 

 hinder side very broad, squarish, yet rounded. Posterior dorsal 

 margin straightish, only a trifle oblique ; anterior a little concave 

 near the beaks, then feebly curved and suddenly descending. 

 Ventral outline arcuate, considerably upcurving in front. Surface 

 concentrically finely striated, somewhat uneven through periodic 

 interruptions of growth. IJmbones small, contiguous, incurved, 

 pellucid, located in advance of the median line. Hinge-teeth 

 rather strong, posterior of the right valve and anterior in the 

 left stout, subequal, bifid, and the anterior in the former is rather 

 thicker than the hinder in the latter, which is sublamellar. Muscular 

 scars somewhat small, deepish, subequal. Interior of the valves 

 not very glossy, roughish. 



Length 15 miUim., height 14, diameter 8|. 



HcA. West Island, Prince of Wales Channel, Torres Straits, 7 fms. 



This is rather a solid species and peculiarly acuminated at the 

 extremity in front, with rather conspicuous lines indicating periodic 

 growth, 



44. Diplodonta sublateralis. (Piate VII. fig. K.) 



Shell very inequilateral, much broader behind than in front, 

 scarcely longer than high, moderately inflated, white, finely concen- 

 trically sculptured with the Unes of growth. Posterior dorsal 

 margin nearly horizontal, straight at first, then gradually curving 

 into the broadly arcuate lateral outline. Pront dorsal edge some- 

 what oblique, scarcely recurved near the beak, but afterwards 

 rounding into the side margin, which is very much more suddenly 

 curvate than at the opposite end. Ventral margin more sharply 

 arched than the posterior, but less so than the anterior. Umbones 

 small, acute, only slightly elevated, situated far in advance of the 

 centre. Hinge-plate narrow in the right valve, conspicuously 

 grooved in front of the two cardinal teeth ; of these the anterior is 

 very smaU, lamellar, and falls perpendicularly beneath the beak 

 the posterior being about three times as thick and deeply bisected. 

 The ligamental furrow is narrow and 5| millim. in length. The 

 muscular scars are subequal, the posterior a trifle broader. Length 

 19| miUim., height 18^, diameter 10. 



Hah. Torres Straits, 7-10 fms. 



Only a right valve of this species was obtained by Dr. Coppinger 

 which, however, is apparently distinct in form, the chief distin- 



