146 PALEONTOLOGY OP NEW-YORK. 



REMARKS ON THE GENERA PRODUCTUS AND STROrHALOSIA. 



Among the genera of the Family PRODUcxiDiE, there are recognized at 

 the present time the following : Chonetes, Productds, Strophalosia and 

 AcLOSTEGES ; the two latter being considered by Mr. Davidson as sub- 

 genera of Prodcctus. 



The Genus Chonetes has already been noticed in the preceding pages ; 

 and from its marked characters, there is usually little danger of con- 

 founding it with any other of the Productida3. The Genus Productus, in 

 its typical and varied forms, is characteristic of the Carboniferous period : 

 a few species are known in the Permian, while other similar forms in the 

 Devonian, which were formerly considered as Ppoductus, have lately 

 been referred to the genus or subgenus. Strophalosia of Prof. King. 



Productus, which is the oldest established genus, includes species 

 described as semicircular or semioval concavo-convex shells, with spini- 

 ferous exterior surface, straight hinge-line, without an area on either 

 valve, and without teeth or sockets. The interior characters, though with 

 a general resemblance to Strophodonta, have in addition certain other 

 points by which they are distinguished. Notwithstanding that the spe- 

 cies of Productus have usually the shell more or less closely studded 

 with spines, and generally a row of spines just below the hinge-margin 

 of the ventral valve, there are some species referred to this genus which 

 are nearly destitute of spines, and others upon which no spines have 

 been detected except on the ears or near the cardinal margin. Species 

 having this exterior character are usually more extremely gibbous or 

 ventricose in the ventral valve than any species of Lept^na, Stropho- 

 donta or Chonetes, and the dorsal valve is more deeply concave. 



Strophalosia is described as differing externally from Productus in 

 sometimes having a truncate apex, and by the presence of an area of 

 greater or less extent on each valve, with a foramen which is more or 

 less closed by a deltidium. In the interior, it is said to be characterized 

 by teeth in the ventral valve and teeth-sockets in the opposite valve ; 



