100 
Grnus.—ISOCARDIA. 
Lquivalve, heart-shaped, ventricose ; beaks very dis- 
tant, divergent and spirally turned to one side ; 
hinge with two primary flattened teeth situated 
under the beak, and with an elevated lateral one 
under the external ligament. 
I. Cor. Lam. 1.—Turt. B. p. 193. t. 14.—F. p. 
419.—Cuama C. Inn. 11387.—D. p. 212.— Ch. f. 483. 
—H. t. 232. f. 1.—Blain. t. 69. f. 2.—Don. 4. t. 
134.—Pen. 4. p. 214.—Mont. p. 134. and Sup. p. 
50—Lin. T. 8. p. 91.—Turt. D. p. 32. f. 17.—Wern. 
Soc. 1. p. 385. t. 48. f. 483.— Heart-shaped, globose, 
fulvous under a reddish epidermis, nearly smooth ; 
the beaks paler, twisted into a single flat volu- 
tion, both fronting the hinder side. 4...3%. Dublin’ 
Bay. 
TrIBE.—ARCACEA. | 
Teeth small, numerous and disposed in each valve in @ 
line, which is either straight or interrupted ; the 
teeth mutually inserted. 
Genus.—ARCA. 
Transverse, subequivalve, inequilateral; beaks remote, 
separated by the area of the ligament ; hinge linear 
