TRIBE MACTRACEA. 35 



CRASSATELLA. 



Inequilateral, suhorhicular or transverse, closed ; primary teeth 

 two, someirhat divergent, with a hollow at the side ; no lateral 

 teeth, nor obsolete ones; ligament internal, inserted in a pit in 

 each valve. 



C. KiNGicoLA. Lam. 1. — Sow. G.f. 2. — Reeve. Ic.f. 5. Ovate- 

 orbicular, sub-gibbous ; yellowish-white under a brown epidermis, 

 obsoletely rayed, with delicate transverse striae, the beaks plaited. 

 3. — Nero Holland. 



M. Edulis. Gray. Mag. N. H. 1837.— Mact. E. Z. J. 5. 

 p. 335. (jjoung?) Ovate, thin, white, smooth, covered with a thin 

 olive or reddish epidermis, forming two raised edges on the anterior 

 slope: anterior slope white ; lateral teeth short, triangular. 2.. 2^. 

 — Port Famine. 



* * * Anterior slope simple. 



M. Byronensis. Gray. — Beech. Z. t. 44. /. 11. Ovate, 

 slightly triangular, white, rather solid ; lateral teeth short and 

 rounded, (thinner when young).— >Si. America. 



M. ExALBiDA. Gray, in Mag. N. H. 1837. Ovate-oblong, 

 white, rather thick ; umbones sub-anterior : lateral teeth short and 

 thick, the posterior one sub-tubercular.— *Sf. America. 



M. Edults. Gray. 3Iag. N. H. 1837.— Mactra E. King. 

 Z. J. 5. Sub-triangular, tumid, smoothish, squalid fulvous ; 

 inside white, the lateral teeth prominent. 2..2|. — Port Famine. 



M. Lateralis. Gray. — Mactra L. Say. Jour. A. N. S. 

 Phil. 2. p. 309.— Gould. Mas.f. 34, 5.— Conr. Am. C. t. 14./. 2. 

 Triangular, very convex, nearly smooth ; lateral margins flattened, 

 cordate, with a straight sometimes concave profile, one rounded at 

 the tip, the other longer and less obtuse : umbo sub-central, pro- 

 minent, i- -^f. — U. States. 



The shell, at present the sole representative of Mr. Gray's genus 

 Gnathodon, cannot strictly be included under any of the La- 

 marckian genera, it comes tolerably close however to Mactra. 



GNATHODON. Gray. 



Sub oval, equivalve, inequilateral, covered with an olive green 

 cuticle, generally a little decorticated at the umbones ; a lateral and 

 two cardinal teeth in one valve, two cardinal and two lateral in the 

 other, the ligament in an intervening pit : sinus of the muscular 

 scar small. 



G. CuNEATus. Gray. Mag. Nat. 1837. — Sow. G. — Reeve, 

 t. 43. 



