BEEDE AND ROGERS.| Coal Measures Faunal Studies. 323 
Nomenclature. 
This is particularly true of such species as Productus longis-* 
pinus Sow., which some authors are inclined to divide into two 
species, as well as to remove it from the genus Productus. In 
the following lists this species and its near relative, Productus- 
muricatus N and P., will be referred to under the subgenus 
Marginifera, in accordance with a growing custom, though it - 
is done with considerable hesitancy at this time, as the material : 
in our hands seems to show that the wall surrounding the 
visceral cavity of Marginifera may be but a senile character of’ 
the later species of Productus. For instance, we have never 
seen it in specimens of Productus semireticulatus Mart. from 
. the lower horizons, but in the Permian specimens occur with’ 
this murication well developed, so that they would fall under 
the definition of Marginifera, so far as that character is con- 
cerned, and remove it from the genus, while specimens of the 
same specific type from below, or younger specimens, though 
adult, from the Permian, would fall in the genus Productus. 
For this reason the reference of the species mentioned to Mar- 
ginifera is provisional until the matter has been further studied. 
and the real significance of the character determined. | 
The identifications are provisional in some cases and subject 
to change upon further study. In several cases the nomencla- - 
ture employed here differs from that used in the preliminary: 
papers. For instance, Doctor Girty has shown that Allorisma ~ 
terminale Hall is identical with A. subcuneatum M. and H., and 
antedates it; that orbicularis is the term to be applied to our 
species of Cletothyris. On the other hand, we are unable to 
see some questions in his light; as, for instance, the proper 
term to be applied to Seminula argentea (Shep.). So far as 
Shepard’s original description is concerned it may be open to 
question. The salient features of it were given by Girty?** and 
are as follows: A shell “whose surface is delicately striated, 
and of a silvery-white color and of a strong pearly luster.” It’ 
seems to us that this description would characterize this species “ 
among any Coal Measures brachiopod fauna where it is abun- 
dant. This is particularly true where the specimens are freshly 
broken from limestone, or are freshly exfoliated or bruised, 
when it has the striated appearance as well as the pearly luster 
described by Shepard. It is true that the surface of perfect 
Specimens is bare of striations, but in breaking them from 
268. U.S. Prof. Pap., 16, p. 406, 1903. 
