NOTICE OF PALEONTOLOGY OF NEW YORK. 177 



which has the apex truncated and the surface of the ventral valve orna- 

 mented with spines, but having the vascular markings peculiar to the 

 genus. 



Under the head of Productus and Strophalosia, the relations of these 

 genera and of the Genus Aulosteges are discussed. The Devonian 

 species, sometimes referred to Strophalosia, are shown to have a narrow 

 area, but with internal vascular impressions like Productus. The 

 absence of an area in the Genus Productus is not uniform, as is shown 

 in P. costatus of the Carboniferous system in America ; and the same has 

 been shown by Mr. Davidson to be true of P. sinuatus and P. semireticu- 

 latus of Europe. 



In comparing the American Devonian forms of Productidse with the 

 Strophalosia of the Permian system, the former have a greater width 

 on the hinge-line, and in this respect more resemble typical Productus; 

 while the narrow cardinal area and hinge-teeth assimilate them with 

 Strophalosia. Notwithstanding this feature, the vascular markings are 

 hke Productus. 



At this epoch we have the earliest known appearances of these forms, 

 the type of which becomes extravagantly developed in the Carboniferous 

 period, and waning during the Permian epoch, is presented for the most 

 part in degenerate modifications of the typical forms. Although we 

 cannot shut our eyes to this fact of development to what may be termed 

 the perfection of the type, and its more abrupt decline, we are either 

 compelled to extend the characters of Productus so as to cover the two 

 forms or modifications indicated, or else to propose a distinct designation. 

 The latter course has been adopted, and the name Productella is pro- 

 posed for the strophaloid Productids of the Devonian period. 



The Subgenus Productella is compared as follows, in Pal. N. Y., Vol. 

 IV, page 153 : 



" These shells differ from Strophalosia iu the extremely narrow linear car- 

 dinal area, greater extension of the hinge-line, more extreme arcuation or 

 yentricosity of the ventral valve iu many or most of the species, and especially 

 in the direction and termination of the renform vascular impressions, which 

 resemble those of Aulosteges and of some species of Productus. It differs 

 from Productus in the constant presence of an area, hinge-teeth and sockets." 



Under this genus are enumerated and described, from the Upper Hel- 

 derberg and Hamilton groups, the following species : 



Cab. Nat. 23 



