68 GENUS XI. SPONDYLUS. 



Lamarck divides these into two genera, as follows : 

 Spondylus. Shell inequivalved, eared, and rough or spinous, 

 ^vith unequal beaks, the inferior more produced, with a 

 flat triangular face, parted by a groove ; the hinge with 

 two strong recurved teeth, and an intermediate hollow 

 for the reception of the cartilage ; one muscular impres- 

 sion QSpondylus Gaderojms Linn. See pi. 3. f. 29). 

 Plicatula. Shell inequivalved, without ears, the beaks un- 

 equal, without a face, having folds on the margin ; hinge 

 with two strong teeth in each valve, and an intermediate 

 hollow for the reception of the cartilage ; one muscular 

 impression in each valve (Spondylus plicatus. See pL 3. 

 f. 30). 



