CONCHOLOGY. /O 



with a large triangular slope in the middle ; articulation trans- 

 verse, straight, and by two distant lateral condylse. Ten species. 

 Fossils only. 



5. Genus Plicatula. 

 Animal. Unknown. 



Shell. Solid, adhering, subirregular, inauriculated, inequivalve 

 pointed at the summit, rounded and subplicated posteriorly ; in- 

 ferior valve without heel ; hinge cephalic, longitudinal, provided 

 upon each valve with two strong teeth, entering in corresponding 

 cavities ; ligament altogether internal and inserted in a median 

 cavity. Inhabits the American seas. Five species. 



Plicatula ramosa. Plicatula cristata. 



P. depressa. P. Australis. 



P. reniformis. 



6. Genus Spondylus. 

 Animal. Body moderately compressed, provided inferiorly 

 with a rudiment of a foot, without byssus ; mantle open in all its 

 inferior and superior portion ; mouth surrounded with very thick 

 and fringed lips. 



Shell. Solid, adhering, subregular, more or less spined, sub- 

 auriculated, inequivalve ; the right or inferior valve fixed, much 

 more excavated than the other, and having posteriorly at the 

 summit a triangular face enlarging, and elongating with age ; 

 hinge longitudinal, provided in each valve, with two strong teeth 

 entering corresponding cavities ; ligament short, nearly median, 

 partly exterior ; muscular impression single and subdorsal. Found 

 in all the seas of hot climates, and even in the Mediterranean. 

 Four of five fossils are found in France, one in South America, 

 Twenty-one species. 



*Spondylus Americanus. Spondylus gsedaropus. 



S. candidus. S. arachnoides. 



S. coccineus. S. multilamellatus. 



S. spathuliferus, S. crassisquama. 



S. longitudinalis. S. ducalis. 



S. costatus. S. violascens. 



