PART II. ATBACHIA. OSTBACIDJB. 38.9 



OSTBEA 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. spondyloideum. Sow. Gen. f. 1 5. 



Dendrostrcea 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. Ib. 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. Ib. f. 1. 

 Virginica. Ib. f. 1. 



Gryphcea 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. incur va Ofy.130.) Sow. Gen. f. 2. dilatata. Ib. f. 3. 



Plicatula 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. 12Q. 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 



