CONCHOLOGY. 



81 



S. longitudinalis. S. crassisquama. 



S. costatus. S. ducalis. 



S. longispinous. S. violascens. 



S. regius. S. microlepos. 



S. variegatus. S. crocens. 



S. avicularis. S. radians. 



S. zonalis. S. aurantius. 



S, Araericanus.* 



8. Genus Podopsis. PI. IX. 



Animal. Unknown. 



Shell. Subregular, somewhat thick, equilateral, symmetrical* 

 inequivalve, adhering by the extremity of the shorter valve ; the 

 other terminating in a pointed, reflexed, and median summit. 

 Two fossil species, 



FAMILY XIX. 

 OsTRACEA. Six genera. 



1. Genus Ostrea. PL IX. 



Animal. Body compressed, more or less orbicular ; edges of 

 the mantle thick, not adhering or retractile, and provided with 

 a double row of short and numerous tentacular filaments ; two 

 pairs of elongated and triangular labial appendages ; a subcentral 

 bipartite muscle. 



Shell. Irregular, inequivalve, inequilateral, roughly foliaceous, 

 the left or inferior valve adhering, larger and deeper than the 

 other, its summit prolonged with age into a sort of heel; the right 

 or superior valve more or less operculiform ; hinge oral, toothless ; 

 ligament subinterior, short, inserted in an oblong cardinal cavity 

 increasing with the summit ; muscular impression single and sub- 

 central. Found in all seas near the mouths of rivers. Defrance 

 enumerates one hundred and twenty species. Lamarck thirty- 

 three fossil, forty-nine living. 



Ostrea edulis. Ostrea ruscuriana. 



