SUPPLEMENT TO THE BIVALVIA. 3 
irregularly ridged by simple lines of growth. Connexus ligamentous ; impression by the 
mantle with scarcely a perceptible sinus. 
This genus is closely connected with Cyc/as, 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 Zit/orine. 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 
im 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. fluminailis, 
Mill.) is quoted by Mr. De la Condamine as having been found at Charlton in association 
with C. cuneiformis, Melania inquinata, &e. 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 Cordicula, to include those 
species which have elongated lateral teeth, striated in a transverse direction and a 
somewhat imbricated exterior, taking Tel/ina fluminalis, Miler, 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, 6. 
Cyrena crassa, Desh. Coq. Foss. des Env. de Par., p. 119, pl. xviii, figs. 14, 15, 1824. 
—  (corpicuLa) crassa, Sandberger. Land- und Siissw.-Conch., p. 252, t. xiv, 
figs. 4, 46, 1872. 
Spec. Char. C. Testdé crassa, cordiformi, sublevigatd, nitiauld ; umbones parvuli, 
submediani ; lunuld parva, paulo profundd, obsolete circumscriptd ; dentes cardinales bint 
bifidi et unicus simplex, nec non laterales inequales, crenulis rectis plicatuli in utraque 
valvd extant. Impressione pallii breviter sinuosd. 
