Dr. J. E. Gray on some Families of Bivalve Shells. 39 



striated, anterior very large, angular, hinder elongate, compressed. 

 V. Cyprinoides. 



4. Cyrena, Lamk., Gray, P. Z. S. 1847, n. 553. Shell sub- 

 cordate ; lateral teeth smooth, front roundish, hinder rather 

 compressed. C. Zeylanica, 



B. Cardinal teeth 2 • 2, moderately diverging, front of right valve 

 and hinder of left valve smaller ; lateral teeth elongate, com- 

 pressed, smooth ; of right valve double, of left valve simple. 

 Shell thin. 



5. Sphcerium, Scopoli, Gray, P. Z. S. 1847, n. 555. Shell 

 oblong, cordate, equilateral; siphon of animal separate, diver- 

 ging at the tip. S. corneum. 



6. Pisum, Megerle, Gray, P. Z. S. 1847, n. 556. Shell ovate, 

 wedgeshaped, inequilateral, truncated behind ; siphons of animal 

 short, united to the end. P. amnicum. 



Fam. 6. Cyrenellad^. 



Shell oblong, roundish, ventricose, thin, covered with a hard 

 olive periostraca. Cardinal teeth 3 • 2, the front and hinder of 

 the right valve thin, laminar, united above under the umbo and 

 enclosing the small triangular central one ; the two teeth of the 

 left valve united above under the umbo, and fitting into the very 

 narrow slit between the central and two united teeth in the other 

 valve ; the front tooth the longest, large and high, especially in 

 the middle of its length, and oblique ; the hinder small, thin, 

 and diverging from the umbo ; front lateral teeth none, hinder 

 rudimentary, elongate, the one of the left valve being separated 

 from the dorsal margin by a slightly impressed groove. Siphonal 

 inflection none. 



Animal : — mantle lobes free beneath, united at each end, and 

 furnished with two elongated, united, contractile (not retractile) 

 siphons; lips elongate; foot subcylindrical, clubshaped. Gills 

 two on each side (in Lucinida only one) (Mag. Zool. 1835, t. 70). 



Genus 1. Cyrenoida, Gray, Proc. Zool. Soc. 1847. 



Cyrenoida, Joannis, Mag. Zool. 1835, t. 64 (shell). 



Cyrenella, Deshayes, Mag. Zool. 1836, t. 70 (animal) ; Wieg- 

 mann's Archiv, 1836 ; Desh. Elem. Conch, t. 14*. 



Cyrenodonta, Auct. ? 



Cyrenoides, Sow. Manual, ed. 2. 135. 1842, misprint. 



This genus was established by Joannis (Mag. Zool. 1835, t.64), 

 who veiy inaccurately observes, — " Le charnier qui est pour lea 

 dents cardinales a-peu-pres celle des Cyrenes, mais qui manque 

 corapletement des dents laterales si caracteristiques dans ces 

 dernieres, nous a decide k, etablir le sousgenre Cyrenoide." The 

 figure is more accurate than this description. *. 



