BIVALVIA. - 201 



Petricola coralliophaga, Desh., ' Coq. Foss. des Env. de Par.,' resembles one form 

 of our variable shell, but from description the dental apparatus appears diflferent. An 

 individual, apparently of this genus, is in the cabinet of my friend Mr. F. Edwards, 

 and found at Barton, but it is in so deplorable a condition that no fair comparison 

 can be instituted. 



Tapes.* Megerle, 1811. 



Venus (sp.) Linn. 



Callista, Callistoderma (sp.) Poll, 1791. 



Tapes. Schum., 1817. 



Pbllastea. G. B. Sow., 1827. 



Venerupis (sp.) Flem., 1828. 



Saxidomus? Co7irad, 1837. 



Gen. Char. Shell equivalve, transversely oblong, ovate, or subtriangular, inequi- 

 lateral, closed, and generally somewhat thick and strong ; posterior side the larger ; 

 externally smooth, striated, or decussated ; inner margin free from crenulations. 

 Hinge composed of three sub-parallel cardinal teeth, two of which are bifid. Palleal 

 sinus large and deep. Ligament external. 



Animal of an oblong form, having the mantle freely open in front; the margins 

 plain, or sometimes fringed with fine filaments ; siphons sometimes separated to their 

 bases, at others united for half their length, with their orifices bordered by cirrhi ; foot 

 lanceolate and thick, furnished with a byssal groove. 



This is an extensive genus, and species that may be referred to it have been 

 obtained from the seas of all climates, some of which are extremely elegant, and in the 

 recent state are beautifully ornamented. Many fossils from the older rocks, strongly 

 resembling in form the recent genus, and possessing a mantle mark indicative of the 

 possession of siphonal tubes, have been considered as entitled to a generic association ; 

 the distinctive characters, a byssal groove in the foot of the animal, of course is in the 

 fossil perfectly useless, but the shell also possesses a good distinction in the peculiar 

 arrangement of the hinge denticles ; this, however, is another character seldom of 

 much service in the older fossils, and it is only when we come into the Tertiaries that 

 we are quite sure of its existence, and in the oldest of these it is doubtfully present. 



1. Tapes virginea, . Tab. XX, fig. 1 a — e. 



Vends virginea. Mat. and Rack. Linn. Trans., vol. viii, p. 89 t. ii, fig. 8, 1807. 



— — Turt. Brit. Biv., p. 156, pi. 8, fig. 8, 1822. 



— L.'ETA. Poll. Test. Utrusq. Sic, t. xsi, fig. 1. 



— RHOMBOiDES. Peiin. Brit. Zool., vol. iv, p. 9 7, pi. Iv, (fig. right hand.) 



— SAENiENSis. Turt. Brit. Biv., p. 153, pi. x, fig. 6, 1822. 



* Etym. Tair^s, tapestry, probably so called from the ornamental exterior of most of the species. 



