EEPORT ON THE LAMELLIBRANCHIATA. 65 



but in other respects they agree witli the normal Australian form, except that the 

 umbonal angle is rather less acute. 



Myodora crassa (Stutchl)ury). 



Anatina crasm, Stutchburv, Zool. Journ., vol. v. \\. 100, Tiili. Su|ipl. xliii. figs. .5, G. 

 Mijodora crassa, Reeve, Proc. Zool. Soc. Lond., 1844, p. 92. 

 Mi/odora crassa, Reeve, Conch. Icon., fig. 1. 

 Myodora crassa, Hanley, Roc. Biv. Shells, pi. x. fig. 6. 

 Myodora crassa, Smith, Proc. Zool. Soc. Lond., 1880, p. 581. 



Habitat. — Port Jackson, Sydney, iu 2 to 10 fathoms (Challenger, Stutchbury, 

 Macgillivray, King) ; Middle Hai'bour (Angas). 



Only one not quite full-grown right or deep valve was obtained by the Expedition. 

 The species, although small, is remarkable for its solidity, and the less flattened character 

 of the flat or left valve. The microscopic sculpture is fairly coarse, the radiating striae 

 being well marked. In addition to the single valve above mentioned, I have since 

 discovered three very small odd valves which possibly may be the young state of this 

 species. I find in them two ditferences, namely, a larger pallial sinus and no lateral 

 dental grooves in the right valves. Considering, however, the modifications in the 

 hinges of some bivalve shells resulting from age, I think it very possible that these 

 differences in the present instance may arise from a like cause. 



Myodora trigona, Reeve. 



Myodora trigona. Reeve, Conch. Icon., fig. 2 ; Proc. Zool. Soc. Loud., 1844, \). 92. 

 Myodora tincta. Reeve, Conch. Icon., fig. 5; Proc. Zool. Soc. Lond., 1844, p. 93. 



Habitat. — Flinders Passage, North Australia, in 7 fathoms. 



A single left valve from this locality diSers from the type from the Philippine Islands 

 merely in having the dorsal margins convergent at a rather less acute angle, so that the 

 form becomes rather more oblong, and a right valve is still less angular and partakes of 

 the form of an adult Myodora oblonga, Reeve. This species may only be the youug 

 form of a variety of that species, being mainly distinguished by rather finer concentric 

 sculpture. 



Myodora sp. 



Te.sta valva sinistra suba^quilaterali, triangulari, latere antico acute angulato, po-stico 

 oblique truncato, leviter concava, sulco prope margiuem dorsi posticum exarata, concentrice 

 sulcata, interstitiis subrotundatis, pone sulcum radiantem obsoletis, undique microscopice 



(zool. chall. EXP. — PART xxxT. — 1885.) Mm 9 



