306 Cincinnati Society of Natural History. . 
SUBCARBONIFEROUS FOSSILS FROM THE LAKE 
VALLEY MINING DISTRICT OF NEW MEXICO, 
WITH DESCRIPTIONS OF NEW SPECIES. 
By 8S. A. Mitter, Esq. 
Prof. E. D. Cope, of Philadelphia, returned from his last annual ex- 
ploring expedition, in the Western territories, with a collection of in- 
vertebrate fossils, from the Lake Valley Mining District of New 
Mexico, which ‘he, very kindly, submitted to the writer for determina- 
tion and definition. They are from rocks of Subcarboniferous age, and 
belong to the Burlington or Keokuk Group, but most likely to the 
former. The following remarks and enumeration of species will — 
all the light, in our possession, upon the age of the rocks. 
1. Strophomena rhomboidalis.—This species, as it is now under- 
stood, is found in the Trenton, Utica Slate and Hudson River Groups 
of the Lower Silurian; in the Clinton, Niagara and Lower Helderberg 
Groups of the Upper Silurian; in the Upper Helderberg, Hamilton and 
Chemung Groups of the Devonian; and in the Waverley, Burlington 
and Keokuk Groups of the Subcarboniferous, in America. It is not 
known to the author higher than the Keokuk. Its Vertical range ex- 
ceeds that of any other species that occurs in these formations, or in 
any other rocks of the known world, and its geographical distribution 
extends to every continent where the strata of these ages have been 
studied and described. Its form is subject to many variations, and 
these have received distinct names in different formations, as S. tenwt- 
striata in the Lower Silurian, 8. depressa in the Upper Silurian, and 
S. rhomboidalis in the Devonian. And, so far as the author has ob- 
served, it would appear that the Lower Silurian specimens are usually 
smaller and have fewer concentric wrinkles over the visceral region 
than those found in the higher strata of the Upper Silurian and” Devo- 
nian formations, and that the length of the front and lateral margins, 
from the geniculation, in the Upper Silurian specimens, is usually 
greater than it is in Lower Silurian, Devonian or Subcarboniferous 
specimens ; but these differences are not so constant as to form infex- 
ible characters, and hence it is that many of the learned and better pale- 
ontologists have classed them all together under the first and oldest 
specific name. On the other hand, the similarity between specimens 
collected in rocks of the same formation in distant countries is re- 
markable. This is most strikingly illustrated by the fact that a 
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