PART II. ATBACHIA. OSTRACID^. 389 



OsTREA Linn. Shell foliaceous^ irregular, generally 

 attached by the under valve ; hinge usually without 

 teeth. 



Pedum Brug. Shell hatchet-shaped, depressed ; in- 

 equivalve, slightly auriculate ; umbones small, re- 

 mote ; sides of the lower valve turned upwards, with 

 a deep sinus for the passage of the substance by 

 which it adheres ; a small, central, spatulate tooth in 

 each valve bears the cartilage, and a transverse cen- 

 tral furrow between the umbones holds the ligament, 

 which spreads also between the umbones. 



P. spondyloideuin. Sow. Gen. f. 1 — 5. 



Dendrostran Sw. Shell irregular, equivalve, attached 



by its lower valve by extraneous processes ; the 



margins solid and plicated. 



D. folium. Sow. Gen. f. 3. crista-galli. Sow. Gen. f. 2. 

 carinata, lb. f. 1 . 



Ostrcea Linn. Shell irregular, round or oval, inequi- 

 valve ; the margins thin and brittle ; no teeth ; um- 

 bones central. 



O. edulis. Sow. Gen. f. 2, cingulata. lb. f. 1. 

 Virginica. lb. f. 1. 



Gryph(jea Lam, Shell regular, 

 inequivalve ; one valve con- 

 vex, with the umbo recurved, 

 the other smaller, and nearly 

 flat; margin of the valves not 

 foliaceous. 

 G. incurva {fig.l'HO.) Sow. Gen. f. 2. dilatata. lb. f 3. 



PUcatula Lam. Shell irregularly ovate, plicated, in- 

 equivalve ; one valve more convex than the other ; 

 cardinal teeth ^ sagittate ; the sides strongly, regu- 

 larly, and transversely grooved ; between the teeth is 

 the internal ligament, (^fig. I29. e.) 



P. gibbosa. Sow. Gen. f. 1, 2. 



Anomia Linn. Shell thin, perlaceous, very irregular, 

 inequivalve ; attached by a calcareous mass, which 



c c 3 



