GENERA PRODUCTUS AND STROPHALOSIA. 245 



;V. REMARKS OX THE GENERA PRODUCTUS, STROPHALOSIA, 

 AULOSTEGES AND PRODUCTELLA. 



[From Vol. IV, PalaBontology of New- York.] ' 



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

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

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

 genera of Productus. 



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

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

 ing it with any other of the Productidge. The Genus Productus^ in its 

 topical 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 Productus, 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 species 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 desti- 

 tute 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 Leptcsna, Strophodonta or Chonetes, and the 

 dorsal valve is more deeply concave. 



■Strophalosia is described as differing externally from Productus in 

 sometimes having a truncated 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 ; while 

 the disposition of the reniform vascular impressions of the dorsal valve is 

 a distinctive feature. 



In reference to the Genus Pro^wc^z^5, Mr. Davidson remarks as follows : 



" All authenticated species of Productus, hitherto examined, have shown them- 

 " selves to be edentulous; but whether this character was general and without 

 '' exception, may remain a question for further consideration : anyhow, the dorsal 

 *' valve must have turned on its hinge-line with as much precision as in Chonetes, 

 "which possessed regularly articulating teeth. It has been often asserted and 

 " believed that Productus might be distinguished from its subgenera by the total 

 "absence of an area; and although this is the prevalent character of the genus, 

 " still in certain species, such as P. sinuatus, a perfectly developed area is generally 

 " present in the ventral valve. There exists also an occasional tendency to the for- 



