ISOCARDIA. 



Genus Isocardia, Lamarck. 

 Testa eequivalvis, cordata, ventricosa, concentrice lirata et 

 striata, umbonibm distantibus, divaricatim symmetrice 



iiirulutis; ratde inreqiiUiitcrulin, /a five aidico breris- 

 simo. Cnrdo : deufibns cardiiwlibim duob/is, ctn.ipn ■, •,■/*, 

 inirantiius, uno sub umbone recurvo, dente laterali unico 

 elongato, postico, infra ligamentum. Ligamentum ex- 

 ternum, angnstum, subelongatwn, h'uic umbones versus 

 bifurcation. 

 Shell equivalve, heart shaped, ventricose, concentrically 

 ridged and striated, with the umbones distant and 

 divaricately, most symmetrically involuted ; very ine- 

 quilateral, anterior side very short. Hinge : two com- 

 pressed cardinal teeth interlocking, one of which is 

 recurved under the umbone, one elongated lateral 

 tooth on the posterior side beneath the ligament. 

 Ligament external, narrow, rather elongated, thence 

 biforked towards the umbones. 

 The genus Isocardia though limited in species is espe- 

 cially distinguished by the very novel and beautiful struc- 

 ture of the umbones ; which, instead of terminating in imme- 

 diate approximation to each other, as in the genus Cardium 

 aud others, divaricate off in an opposite direction and be- 

 come most symmetrically involuted. The bifurcate exten- 

 sion of the ligament is also peculiar. 



Linnaeus included the only species of Isocardia with 

 which he was acquainted, the Isocardia cor, in his genus 

 Cliarna ; and Bruguiere referred it, in company with another 

 species, supposed to be the Chama Moltkiana of Chemnitz, 

 to a place among the Cardites. Lamarck, very properly 

 elevated them to the rank of a new genus, to which several 

 fossil species were added, and his generic name has been 

 universally adopted ; although, according to the strict rules 

 of nomenclature, it is a matter of some question whether 

 it ought to be maintained. 



The Isocardia cor and its anatomy were, in fact, de- 

 scribed some years before by Poli in his beautiful work the 

 ' Testacea utriusque Sicilias ' ; the mollusk under the title 

 of Glossus, and its shell under that of Glossoderma. 



Only five species of Isocardia are at present known ; two 

 of similar character, one British or Irish, the other Medi- 

 terranean, distinguished from each other by their transverse 

 or globose form with a variation in the incurvature of the 

 umbones, and three of like affinity from the Eastern world, 



the specific peculiarities of which arc determined bj varia- 

 tions of form, and by the varied development of the con- 

 centric ridges. 



Species 1. (Mus. Cuming.) 

 Isocardia Moltkiana. hoc testa subquadrato-ovatd, 

 gibbosd, latere antico brevissimo, postico oblique cari- 

 nato : fort it: r concentrice plicato-costatd, cosMs carinam 



super ciiijiirii/s, quasi ubtuso-l ' uhercnlatisjiri d/,i,.\/n ma 

 medio subprodncta, l/triyatd ant subtUissime striata : 

 lutescente-albd. 

 Moltkian's Isocardia. Shell somewhat squarelj ovati 

 gibbous, anterior side very short, posterior obliquely 

 keeled ; strongly concentrically plicately ribbed, ribs 

 conspicuous upon the keel, as if obtusely tuberculated, 

 extreme posterior area rather produced in the middle, 

 smooth or very finely striated; yellowish white. 

 Chama Moltkiana, Chemnitz, Conchy]. Cab., vol. vii. 

 pi. 48. f. 485-7. 

 llah. Sorsogon, Province of Albay, Island of Luzon, Phi- 

 lippines (dredged from among coarse sand and gravel, 

 at the depth of six fathoms) ; Cuming. 

 I have to congratulate Mr. Cuming upon the discovery 

 of a valve and a true pan- of this comparatively lost species, 

 because it enables me to correct a very importanl 

 in the history of tliis genus. 



By referring to the figures, above quoted, of the ' 

 Moltkiana, they will be found to agree with this, and not 

 the well-known species hitherto published under that name. 

 The Isocardia Moltkiana is a short gibbous squarish shell, 

 very strongly plicately ribbed, and the ribs are di 

 with so much force upon the keel as to assume almost the 

 appearance of tubercles. The species which has hitherto 

 supplanted it, and which 1 m>\\ propose to distinguish by 

 the new title of Isocardia vulgaris, is of a 

 form, very finely pncatelj ridged, and the ridges become 

 perfectly obsolete on approaching the keel; all of which 

 differences I consider of spi 



Species 2. (Fig. « and h '.: I 

 Isocardia vi i.i. \ MS. Isoc. test Wong - 



tmo-cvr'i. , icato-liratii, 



