178 PROCEEDINGS OF THE GEOLOGICAL sociEeTy. [Dec. 1, 
in New York in the Tentaculite limestone, and in the Pentamerus 
limestone at Schoharie, &c. 
(13) SrropHomena.—Most of the American geologists have in- 
cluded in this genus all the species usually placed in the genus Lep- 
tena, and such species of Orthis as are related to the Leptene. By 
this arrangement they have left a natural group of shells in the genus 
Orthis, but have created a heterogeneous assemblage in Strophomena. 
European writers have usually run into the opposite difficulty, for in 
defining Leptena neatly, they have thrown into Orthis species vari- 
ously characterized, many of which do not agree with any definition 
of the genus. Both difficulties may be avoided by dividing into 
three genera the species hitherto included in Orthis and Leptena, 
retaining each of those genera as most strictly defined, and throwing 
into the third genus the intermediate species which have been placed 
sometimes in one, sometimes in the other of those groups. For this 
third genus we do not require a new name, as Strophomena was 
originally instituted by Rafinesque for one of the species of this in- 
termediate group. 
Orthis is defined by Dalman and Hisinger as having ‘‘ margo car- 
dinalis rectilineus, latus, foramine deltoideo sub nate valvee majoris. 
Valva major dentibus duobus subcardinalibus internis, longitudinali- 
bus, compressis.”” These characters describe the genus exactly as I 
wish to see it limited, excluding all the species which have the fora- 
men covered by a deltidium, as in O. umbraculum and its allies. All 
Dalman’s species agree with this definition except his O. pecten, and 
perhaps O. striatella, which have the foramen closed. 
M. de Verneuil in his excellent account of the Russian fossils has 
added, as a distinguishing character, that in Orthis the ventral valve 
is convex and does not follow the curve of the dorsal valve, while in 
Leptena the two valves have a similar curvature and are, as it were, 
parallel, the ventral valve being concave (Russie, vol. 11. p. 41). But 
M. de Verneuil has not adhered to these characters in separatig the 
species of the two genera, as in the greater part of his division of 
Orthides recto-striate uni-aree the curvature of the two valves is 
exactly similar, and the dorsal is the concave valve. We are indebted 
to M. de Verneuil for calling attention to the curvature of the valves 
in these groups, as it has hitherto been nearly overlooked; but we 
can hardly adopt it as a distinctive generic character, as in each genus 
there are a few species which differ in this respect from the majority 
of their congeners. 
Strophomena: not knowing where to find Rafinesque’s original 
description of this genus, I can only refer to it in the ‘ Dictionnaire des 
Sciences Naturelles,’ where the description is rather vague; but the 
characters, ‘Coquille équilatérale, réguliére, subéquivalve, ayant 
une valve plate et lautre un peu excayée,”’ added to that of the 
original species, S. rugosa, having the dorsal valve concave, limit us 
to the group of which Orthis umbraculum may serve as the type, and 
distinguish Strophomena from both Orthis and Leptena. 
In a very instructive paper on the arrangement of the Brachiopoda, 
published in the ‘ Annals of Natural History’ for July and August 
