30 CEETACEOUS PELECYPODA 



Shell equivalvc, or nearly so, inflated, closed on both ends, beaks incurved ; hinge 

 Avith one tooth l)clow the umbo in the right valve and two teeth in the left one, the 

 posterior of which is smaller and appears to be only an anterior thickening of the 

 nymplias for the support of the cartilage. Tlie margin of the shell, just behind 

 the beaks, is for a very short distance somewhat thickened for the attachment of a 

 ligament ; no pallial sinus ; mviscular impressions rounded. 



The genus Basterotia was proposed by Mr. Mayer for a tertiary species. Bast, 

 corhiiloides, and first published by the late Dr. M. Homes in his work on the 

 Vienna tertiary Mollusca. Dr. Homes refers to the recent Corbula qtmdrata as 

 being a species very similar in shape to the fossil Basterotia, and probal)ly 

 belonging to the same genus. I have not examined this species myself as to the 

 exact form of the hinge, but it is the type of Recluz' Eiicharis, and tliis author 

 mentions the presence of one oblique large tooth in each valve and an external 

 ligament. The posterior tooth in the left valve Recluz does not notice, but I have 

 no doubt that both forms belong to one and the same genus, as suggested by 

 Homes. I had the opportunity of examining one valve of a species found by 

 Mr. G. Nevill at Ceylon. Its hinge perfectly agrees with the fossil Bastei^otia, and 

 the form of the shell is also very similar, only less tumid and somewhat longer. 

 Recluz (1. cit., p. 168,) describes a third recent species, Euch. cliptica, which is not 

 carinated. The upper tertiary Corbula quadrata, Nyst, (identical with the recent 

 Poromya anatmoides of Forbes, also known under the name of Embla Korenii, 

 Loven,) cannot be, I believe, geuerically identified with Encliaris, as I shall state 

 further on, when spealdng of the genus Poromya. Jurassic forms like Corbula 

 carinata, Buvignier, may belong to Eucharis. 



Speaking of equivalve forms I should also mention the Jurassic Corb. Glosensis, 

 described by Zittel and Goubert (Journal de Conch., 1861, p. 196). The 

 right valve has one large cardinal tooth and the left only a cardinal pit. If this 

 description of the hinge is correct, it would indicate a new genus of the CossvLiyjE, 

 intermediate between Corbula and Eucharis, unless the species is a Quenstedtia. 



5. Pleurodesma, Homes, 1859, (foss. Moll., Wien, vol. ii, p. 43). Shell 

 oblong or quadrangular, equivalve, closed on both sides, one large cardinal tooth 

 in each valve, and a long groove extending along the dorsal margin of the shell 

 for the reception of the cartilage ; there is no indication of the presence of a 

 ligament. This genus has been proposed for a new tertiary shell, PI. Mayeri, 

 which in general form agrees with Eucharis, but differs widely from it by the form 

 of the hinge. 



6. Corburella, Lycett, 1853, (1850?), (Proc. Cottesw. Xat. Club, vol. i, p. S3), 

 was established for a Jurassic species figured by Phillips (Geol. Yorksh., 1835, i, 

 pi. 3, fig. 27,) under the name of Corbula curtansata. Lycett gives the following 

 generic character. " Shell equivalve, thin, inflated, posteriorly attenuated and 

 gaping, anteriorly rounded, hinge with a small depressed subcouical tooth in each 

 valve, and extended, slightly thickened, laminar plate forming a kind of an anterior 

 lateral tooth or process." Ligament and pallial sinus are not noticed, nor are they 

 perceptible in Phillips' figure. As to general form of the shell the genus would 



