122 CORDIFORM. 



cancellated, with denticulated internal margins ; hinge with two 

 cardinal and two lateral teeth in each valve ; of the latter, one near 

 and one remote from the umbones ; muscular impressions lunu- 

 late, two in each valve, united by an entire palleal impression, with- 

 out a sinus. — Obs. This genus, of which only two or three recent 

 species are known, resembles many species of Venus and Cytherea 

 in general form ; but differs in having lateral teeth, and in the 

 palleal impressions which in all the Veneres, &c. is sinuated. 

 From Lucina it may be known, not only by its oval form, but 

 also by the muscular impressions, which, in Lucina are produced 

 into an elongated point ; it will also be distinguished from Tellina, 

 by the want of a posterior fold in the valve, for which that genus 

 is remarkable, C. Fimbriata, fig. 101, is an inhabitant of the 

 Indian Ocean. Several fossil species are found in the recent for- 

 mations, above the chalk, at Grignon and Hauteville. 



CORBULA. Brug. (A little basket,) Fam. Corbulacea, Lam. 

 Conchacea, Bl. — Descr. Inequivalve, sub -equilateral, transverse, 

 gibbose, not gaping ; cardinal tooth in each valve, conical, curved, 

 prominent, inserting its extremity into a pit in the opposite hinge; 

 cartilage attached to the tooth of the smaller valve, and the pit 

 in the larger; muscular impressions, two in each valve, distant, 

 rather irregular ; palleal impression posteriorly angulated. — Obs. 

 The shells composing this genus were placed in Mya by Linnseus, 

 but differ from the true Myae in having a sinus in the palleal im- 

 pression, and a prominent ligamentiferous tooth in each valve, 

 whereas the Myse have but one. The Corbulse are marine, some 

 species inhabiting the British coasts. Fossil species occur abun 

 dantly in green sand, London clay, crag, and corresponding for- 

 mations. Fig. 89. C. Nucleus. 



CORBULACEA. (Corbulees, Lam.) A family of the order Con- 

 chifera Dimyaria, Lam., containing the genera — 



1. Corbula, with a prominent curved tooth. The Fresh- 

 water species has been separated under the name Potamo- 

 mya. Fig, 89. 



2. Pandora. Thin, pearly, no teeth. Fig. 90. 

 CORDIFORM. (Cor, a heart.) Heart-shaped, a term applied ge- 



