292 
PALAEONTOLOGY OF NEW YORK. 
In Strophonella as in Stropheodonta, the earlier representatives possess 
some of the generic characters in an incipient condition. Species are not 
known to occur in faunas earlier than the Clinton, where this group is repre¬ 
sented by (?) S. patenta and S. striata. The latter species is continued into the 
Niagara group, where it is associated with & semifasciata, at Waldron, Indiana. 
The genus is represented in Europe by S. euglypha and S. funiculata. 
Strophonella striata, Hall, of the Niagara fauna, has a deltidium highly devel¬ 
oped in the immature stages of the shell, a prominent deltidial callus, and a 
short row of cardinal denticulations; it is, in fact, in these respects a reversed 
Brachyprion, bearing precisely the same relation to Strophonella in its fuller 
development as that group does to Stropheodonta. The species also presents 
some differences from the later Strophonellas in its internal characters. In 
the pedicle-valve the muscular area is not enclosed, but its lateral margins are 
bounded by two curved ridges continued from the dental plates. In the brach¬ 
ial valve there is a similar arrangement produced by the continuation of the 
crural plates, but the muscular impressions are extremely faint, the radial 
markings of the surface extending quite to the base of the cardinal process. 
Should it be considered useful to recognize the incipient and progressive 
features of the species S. striata, and probably S. patenta, towards a full manifesta¬ 
tion of generic characters, and distinguish them from Strophonella in its more 
mature condition of development, the term Amphistrophia may prove expressive 
of their apparent double relation as shown in the young and mature shells. 
In the other Silurian species of Strophonella the deltidium is more or less 
prominently developed as a convex plate, but in the Devonian these parts assume 
the character they possess in Stropheodonta demissa. In the species of the Lower 
Helderberg and Devonian the muscular area of the pedicle-valve is deeply 
impressed and strongly elevated at the margins, less like that of Stropheodonta 
demissa than that of the later Stropheodontas. In the Lower Helderberg fauna 
are the species S. Headleyana, Hall, S. cavumbona, Hall, S. pundulifera, Conrad, 
S. Leavenworthana, Hall, which possess all the typical features of the genus. It is 
probable that Strophomena radiata and S. Conradi, Hall, belong to the same genus, 
but their interior characters are not fully known. In the Upper Helderberg we 
