124 28 



In Reevk's diagnosis, and in the descriptions of A. clathrala given by later 

 authors, I do not find any mention of several distinctive characters, peculiar to this 

 species. Thus, in the specimens from the Gulf of Siam, the sculpture is diflerent 

 on the two valves; on the right valve it is only the 8 — 10, most anterior ribs which 

 are set with regularly-arranged, small nodules which gradually disappear almost 

 completely from the rest of the ribs; also, on the right valve, all the ribs are 

 somewhat flatter than are those on the left valve. The latter is more strongly 

 sculptured, and on the 18 — 20 most anterior ribs the small nodules occur regularly 

 and distinctly, like strings of beads; but they are frequently absent from the most 

 posterior ribs. Upon both the umbones there is a distinct median groove, which 

 occurs in all the specimens, from the smallest to the largest, and which affords a 

 good distinguishing feature by means of which they may be separated from forms 

 nearly related to them. A. H. Cooke' considers A. rotundicostnta, Reeve, to be 

 synonymous with the present species. I believe the same is the case with A. Troscheli, 

 Dunker.^' Edg. Smith ' doubts Reeve's statement that the epidermis is "very finely 

 bristly between the ribs;" but among the specimens from the Gulf of Siam there 

 are several in which this can be seen, and the bristles in such cases, are parti- 

 cularly strongly developed between the most posterior ribs. Specimens, however, 

 also occur, with a perfectly well preserved epidermis, from which these bristles 

 are entirely absent. As the present species is provided with a byssus, it cannot be 

 referred to the sub-genus Anadara, but must belong to Scapharca.^ The Siam 

 Expedition brought home several specimens in spirit which show a well-developed 

 byssus. 



Area (Scapharca) consociata, E. Sm. 



Area {Scapharca?} consociata, Eug. A. Smith, Challenger Exped. Report on the Lamellibranchiata, 1885, 



p. 266, pi. 17, lig. 7. 



— — — Martini u. Chemnitz, Conchyl. Cabin, Vlll, 2 Abth., p. 221. 



— consociata, Edu. A. Smith, Ann. and Mag. Nat. Hist , 7 Ser., vol. 14, 1904, p. 12. 



W. of Koh Chuen, soft clay {^^h young specimens). S. of Koh Samit, 30 fathoms, 

 mud ('/s). Off Tung Kaben, 6 fathoms, clay mixed with sand Qh). Sound of Koh 

 Chang, 4—5 fathoms, soft clay (3 4- ''/2). West coast of Koh Chang, 10 fathoms, 

 mud (1). E. of Koh Mak, 20 fathoms, mud (2). Between Koh Kahdat and Koh 

 Kut, (5 fathoms, clay mixed with sand (^/a). 



Long. 2—38 mm. (long. 38, alt. 27. — long. 26, all. 18). 



Distribution: Off Chedubar (Aracan coast, 20 30 fathoms, Smith). — 

 Arafura Sea (Smith). 



As may be seen from the measurements given above, Edg. Smith is right in 

 believing that his specimen with a length of 125 mm., collected during the Chal- 

 lenger Expedition, is not full-grown. 



' Annals and Magazine of Nat. Hist. 5 Ser., vol. 18, 1886, p. 95. 



- Index MoUuscor. mar. Japonici, p. 234, pi. 14, figs. 14 — 15. 



=> Proc. Zool. Soc. London, 1891, p. 432. 



' EiHi. A. Smith, who, in the Challenger Report, 1885, refers A. clallirata to the sub-genus Scapharca, 



ill 1891 (loc. cit. p. 432j had changed his opinion, and placed it under Anadara. 



