﻿SUPPLEMENT TO THE BIVALVIA. 



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irregularly ridged by simple lines of growth. Connexus ligamentous ; impression by the 

 mantle with scarcely a perceptible sinus. 



This genus is closely connected with Cyclas, but it differs in having a thick and 

 heavy shell. Its habitation, like the latter, is for the most part in fresh water, although it 

 is found in estuaries in association with Oysters and Littorina. In the recent state it 

 is known only in tropical or subtropical regions, although one species, a remnant of 

 this race, flourished in Britain during the Crag and earlier part of the Glacial, and again 

 in the Post-glacial period, but I am not aware of any of the older Tertiary species having 

 survived to the present day. In the Quart. Jour. Geol. Soc. for 1850, vol. vi, p. 444, 

 Cyrena trigonula, Wood, the Crag and Post-glacial species just referred to {C. fluminalis, 

 Mull.) is quoted by Mr. De la Condamine as having been found at Charlton in association 

 with C. cuneiformis, Melania inquinata, &c. I have not, however, been able to see the 

 specimen so referred by him, and think that the species referred to must have been that 

 described (postea p. 190) as C. trigona, Desh. C. Gravesii is also given by the same 

 author; but I have been equally unable to identify that reference by any British 

 specimen, and Mr. Whitaker's notice of the same species in his list, page 577 of the 

 ' Geol. Survey Memoir,' vol. iv, is, he informs me, inserted on the authority of Mr. 

 De la Condamine's paper only. 



Cyrena as proposed by Lamarck has been separated into numerous sections or 

 subgenera, but most of these divisions appear to me to be no more than might be 

 expected between species. Dr. Gray proposed the name of Corbicula, to include those 

 species which have elongated lateral teeth, striated in a transverse direction and a 

 somewhat imbricated exterior, taking Tellina fluminalis, Miiller, as the type ; retaining 

 Cyrena for those species in which these teeth are not striated, and Batissa, Adams, for 

 some intermediate forms. Several other divisions have also been made, but as I 

 agree with M. Deshayes in thinking that all the various forms of Bivalves possessing two 

 cardinal teeth and two more or less elongated laterals found in the Lower Tertiaries 

 belong to one genus, Cyrena, I have followed his arrangement. 



1. Cyrena crassa? Deshayes. Tab. A, fig. 10 a, b. 



Cyrena crassa, Desh. Coq. Foss. des Env. de Par., p. 119, pi. xviii, figs. 14, 15, 1824. 

 — (corbicula) crassa, Sandberger. Land- und Siissw. -Conch., p. 252, t. xiv, 



figs. 4, 4 b, 1872. 



Spec. Char. C. Testa crassa, cordiformi, sublavigatd, nitiauld ; umbones parvuli, 

 submediani ; lunula parvd, paulo profunda, obsolete circumscripta ; denies cardinales bini 

 bifidi et unicus simplex, nec non lateralis inaquales, crenulis rectis plicatuli in utrdque 

 valvd extant. Impressione pallii breviter sinuosd. 



