GENERA OF SHELLS. 49 



SUS, flavidulus, plica, glaber, sulcatus, virgo, unicolor, gri- 

 seus, distans, Isabella, — concentricus, Pealii, ornatus, dis- 

 locatus. 



(b.) Ears unequal. 

 P. nodosus, pallium, pes felis, tigris, imbricatus, histri- 

 onicus, sauciatus, opercularis, lineatus, flabellatus, irradians, 

 flexuosus, inflexus, dispar, quadriradiatus, Islandicus, asper- 

 rimus, senatorius, aurantius, florens, varius, sanguineus, sin- 

 uosus, ornatus, pellucidus, Tranquebaricus, gibbus, minia- 

 ceus, pusio, hybridus, sulphureus, lividus, hexactes. 



Plicatula. Shell inequivalve, without ears, 

 attenuated at base, superior margin plaited, 

 rounded ; beaks unequal, and without exter- 

 nal facet. Hinge with two strong teeth on 

 each valve ; a pit between the two teeth, re- 

 ceiving the ligament, which is entirely exte- 

 rior. 



The plicatula differs from the pecten by having car- 

 dinal teeth, and being without ears, and from spon- 

 dylus, by having no external facet and no spines. 



P. ramosa, depressa, cristata, reniformis, australis. 



Spondylus. Shell inequivalve, adherent, 

 eared, spiny or rigid ; beaks unequal ; inferior 

 valve presenting a cardinal area external, flat- 

 tened, divided by a fissure, which increases 

 with age. Hinge with two strong cardinal 

 teeth in each valve, with an intermediate liga- 

 mentary fossa connected by a sulcus to the 

 external fissure ; ligament internal. 

 4 



