Report on the zoological collections made in the Indo-Pacific Ocean ...

104 COLLECTIONS PKOM MELAITESIA.in form, the more usual outline being represented by Reeve's fig.47 h, which he wrongly ascribes to the West-Indian species. Thedifference in the angle of divarication of the ridges is at once seenby comparing the two figures 47a and 47 h.43. Diplodonta subcrassa. (Plate VII. figs. I, II.)Shell roundly subquadrangular, only moderately inflated, thickish,decidedly inequilateral, dirty white, not glossy. Anterior sideshorter than the posterior, somewhat pointed at the extremity ;hinder side very broad, squarish, yet rounded. Posterior dorsalmargin straightish, only a trifle oblique ; anterior a little concavenear the beaks, then feebly curved and suddenly descending.Ventral outline arcuate, considerably upcurving in front. Surfaceconcentrically finely striated, somewhat uneven through periodicinterruptions of growth. Umbones small, contiguous, incurved,pellucid, located in advance of the median line. Hinge-teethrather strong, posterior of the right valve and anterior in theleft stout, subequal, bifid, and the anterior in the former is ratherthicker than the hinder in the latter, which is sublamellar. Muscularscars somewhat small, deepish, subequal. Interior of the valvesnot very glossy, roughish.Length 15 millim., height 14, diameter 8|.Hab. West Island, Prince of Wales Channel, Torres Straits, 7 fms.This is rather a solid species and peculiarly acuminated at theextremity in front, with rather conspicuous lines indicating periodicgrowth.44. Diplodonta sublateralis. (Plate VII. fig. K.)Shell very inequilateral, much broader behind than in front,scarcely longer than high, moderately infiated, white, finely concentricallysculptured with the lines of growth. Posterior dorsalmargin nearly horizontal, straight at first, then gradually curvinginto the broadly arcuate lateral outline. Front dorsal edge somewhatoblique, scarcely recurved near the beak, but afterwardsrounding into the side margin, which is very mu.ch more suddenlycurvate than at the opposite end. Ventral margin more sharplyarched than the posterior, but less so than the anterior. Umbonessmall, acute, only slightly elevated, situated far in advance of thecentre. Hinge-plate narrow in the right valve, conspicuouslygrooved in front of the two cardinal teeth ; of these the anterior isvery small, 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. Themuscular scars are subequal, the posterior a trifle broader. Length19| millim., beight 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-