280 
PALEONTOLOGY OF NEW YORK. 
TjEna. In 1844, McCoy, having proposed to apply the term Lept^ena to species 
of Productus or Chonetes or both, suggested a new term, Leptagonia, for shells 
like Produda analoga, Phillips = Leptazna rhomboidalis.* 
There are sufficient reasons for limiting the application of the term Lept^ena 
to shells conforming precisely to the structure exhibited by L. rhomboidalis. 
Dr. Davidson, in his later years, was evidently convinced of the validity of 
this group.f Whether L. rhomboidalis shall be allowed to include all the forms 
from Silurian to Carboniferous faunas which have the characters given in the 
foregoing diagnosis, or whether the numerous specific and varietal names that 
have been proposed shall be recognized in whole or part will depend upon one’s 
conception of specific values. At all events the type of internal structure 
accompanied by the peculiar corrugated and geniculated exterior has proved a 
very compact and resistant combination, a fact evinced by the mere possibility 
of a question arising as to the specific identity of the various forms. It is 
worthy of note that among the American representatives of this type of struc¬ 
ture which have been studied, the extreme differentiation of the muscular area 
as described is even more distinctly exhibited in the forms of the early Car¬ 
boniferous than in those of the Silurian and Devonian. 
Believing that it will serve a good purpose in the taxonomy of these organ¬ 
isms to thus restrict the generic term LepttENA to this peculiar group of forms, 
it will become necessary to arrange under another designation the much more 
abundantly developed “ Strophomenas ” of the Silurian, exemplified by Lep- 
tcma alternata of Conrad. These differ essentially from L. rhomboidalis, not in 
their exterior features alone, but also in their interior characteristics; and there 
is no name among all those which have been suggested or superceded which is 
applicable, or can be legitimately used, and therefore it becomes necessary to 
propose a new generic term. 
* De Vernedil, in 1845, proposed a classification of the species then referred to this genus, on the basis 
of their superficial ornamentation. His conception of the genus is expressed in his own words: “Nous 
proposons de rendre au genre Lept^na, sa valeur primitive, en y reunissant toutes les coquilles plus ou 
moins analogues acelles que Dalman avait ainsi nominees” (Geologie de la Russie, etc., p. 215). We there¬ 
fore find in his list of twenty-three species not only the various types of structure given by Dalman, but 
some others. 
t See General Summary, p. 379. 
