AMPHIDESMA 



Plate I. 



Genus AMPHIDESMA, Lamarck. 

 Testa aquivalvis, inaquilateralis, ohlo7igo-ovalis vel rotun- 

 data, latere postico plenwiqiie breviore, et plus minus 

 flexuoso. Cardo dente miico aut diiobus in utrdque 

 valvd, foveold angustd elongatd interjacente. Liga- 

 mentum duplex, partim tenue, externum, partini eras- 

 sum, in foveold, internum. Impressio muscularis pallii 

 sinii magno. 

 Shell equivalve, inequilateral, oblong-oval or rounded, 

 posterior side generally shorter, and more or less 

 flexuous. Hinge composed of one or two teeth in 

 each valve, with a narrow elongated pit lying between 

 them. Ligament duplex, part thin, external, part 

 thiek, internal, in the pit. Muscular impression of 

 the mantle mth a large sinus. 

 The shells of this genus are chiefly distinguished by a 

 peculiarity in the structure of the hinge, which encloses a 

 strong cartilage internally, within an obliquely elongated 

 pit on the posterior side. The genus as defined by La- 

 marck contained rather a miscellaneous assemblage of 

 species. Some of these liave been transferred to Thracia, 

 some to Mesodesma, and some to Syndosmya ; and several 

 referred to tliis genus by Fleming and others have shared 

 a similar fate. Of the Lamarckian species, A. variegatum 

 {Telliua ohliqua. Wood) may be regarded the ty])e of the 

 genus as now constituted. Mr. Cuming contributed se- 

 veral important new species of this form, from his re- 

 searches in South America, figured by Mr. Sowerby in 

 his ' Conchological Illustrations,' and the species since 

 collected have enabled me to increase their number in the 

 present monograph to upwards of fifty. 



The shells are of an oblong-circular or oval form, with 

 the posterior or cartilage side mostly the shorter, more or 

 less truncated and flexuous. The sculpture consists chiefly 

 of iiTegular concentric ridges, often in densely packed la- 

 raellaj neatly frilled, with the interstices minutely cancel- 

 lated. The species have all a light and delicate aspect, 

 though in several instances rather solid ; some are white, 

 some are painted with rose and pale yellow. There are 

 no British species. The chief localities are Australia, the 

 Philippine Islands, and the western coast of South and 

 Central America. 



Species 1. (Mus. Cuming.) 

 AMPHIDESMA EXARATA. Amph. testd oblongo-ovatd, sub- 



oblique curvala, pellucente, alba, maculis perpaucis ro- 

 seis palUde adspersd, concentrice costatd, costis tenui- 

 bus, subrecurvis, cum interstitiis excavatis, lineis rugm- 

 formibus radiatis. 



The ploughed Amphidesma. Shell oblong - ovate, 

 rather obliquely curved, pellucid, white, faintly 

 sprinkled with a very few rose spots, concentrically 

 ribbed, ribs thin, a little recurved, rayed, together 

 with the deep interstices, with wrinkle-like lines. 



Adams and Reeve, MoU. Voy. Samarang, p. 81. pi. 24. 

 f. 9. 



Hab. Sooloo Sea. 



A subtransparent species, rayed with erect delicately 

 recurved ribs, which, together with the deeply grooved in- 

 terstices, are rayed with wrinkle-like lines. 



Species 2. (Mus. Cuming.) 



Amphidesma pulchra. Amph. testd ovali, pallida, su- 

 perjicie concentrice striata; intus albidd, purpureo 

 varid ; latere postico breviore, margine anticd incli- 

 nutd, striis nonnullis radiantibus, strias incrementi de- 

 cussantibus. 



The beautiful Amphidesma. Shell oval, pale, surface 

 concentrically striated ; whitish within, variegated 

 with purple ; posterior side shorter, anterior margin 

 inclined, rayed with a few striae crossing the striaj of 

 growth. 



Sowerby, Pro. Zool. Soc. 1832, part 2. p. 57. 



Hab. Bay of Caraccas, South America. 



Eesembling A. obliqua, but of mores olid DoHax-MVe 

 growth. 



Species 3. (Mus. Ciuning.) 



Amphidesma venusta. Amph. testd oblongd, transversa, 

 ventricosd, nitidinsculd, sordidi earned, rosea obscure 

 radiatd, latere antico multo lotigiore, rotmidafo, postico 

 subtruncato, ad marginem ventralem flexuoso ; concen- 

 trice sulcatd ; irdus purpurascente, alio limbaid. 



The graceful Amphidesma. Shell oblong, transverse, 

 ventricose, rather shining, dull flesh-colour, obscurely 

 rayed with rose, anterior side much the longer, pos- 

 terior slightly truncated, flexuous at the ventral mar- 

 gin ; concentrically grooved ; purple within, edged 

 with white. 



October, 1853. 



