36 CRETACEOUS PELECYPODA 



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

 with one tooth below 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 

 nymphse for the support of the cartilage. The 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 ; muscular impressions rounded. 



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

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

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

 being a species very similar in shape to the fossil Basterotia^ and probably 

 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' Eucharis, and this 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 Basterotia, and 

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

 Kecluz (1. cit., p. 168,) describes a third recent species. Buck, eliptica, which is not 

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

 Poromya anatinoides of Eorbes, also known under the name of Bmbla Korenii^ 

 Loven,) cannot be, I believe, generically identified with Bucharis, as I shall state 

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

 carinata, Buvignier, may belong to Bucharis, 



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 Coebulinje, 

 intermediate between Corbula and Bucharis, 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, PL Mayeri, 

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

 of the hinge. 



6. Corburella, Lycett, 1853, (1850?), (Proc. Cottesw. Nat. Club, vol. i, p. 83), 

 was established for a Jurassic species figured by Phillips (Geol. Torksh., 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 subcorneal 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 



