Coal Measure Horizon in N. M. — Her rick and Bendrat. 241 
extends throughout the Carboniferous and well into the Per- 
mian with very little perceptible change. While it is possible 
to distinguish several dififerent forms these seem to represent 
different local or stational conditions than any permanent va- 
rietal types. The striae increase in some cases by bifurcation 
and in others chiefly by implantation and considerable varia- 
tion in size and regularity of form was observed but these are 
rather individual than varietal characters. 
*I5. Productiis semireticulatus Martin. 
This well-known shell occurs below the Flint Ridge shales, 
though chiefly in the small form which has been distinguished 
as P. costatus, though it probably does not deserve to be sep- 
arated from the species quoted. xA.bove the Flint Ridge this 
species frequently appears in very large specimens especially in 
the upper or Permo-carboniferous. We have recently found it 
also in the Permian proper. 
*i6. Productns ncbrasccnsis Owen. 
This well-known Coal Measure species is abundant in the 
Flint Ridge shales. It is also sparingly associated with P. 
semireticulatus at higher levels. 
17. Productella pettenuis Meek? 
A small Productella is indicated by imperfectly preserved 
fragments which may belong to the species quoted. 
*i8 Spirifer striatns Martin. 
We have a large collection of spirifers ranging throughout 
the Coal Measures and well up into the Permian which vary 
among themselves in form and many of their surface charac- 
ters. They all agre-e in having an extended hinge and trans- 
verselv-striated hinge area and in the rather sharply angular 
and fasciculate radiating costae. Some display the fine and 
regular concentric lines of growth said by Schuchert to be 
characteristic of S. striatus while others, which have been ex- 
foliated or are, perhaps, in another condition of preservation, 
fail to display these marks. It may be noted that Meek's fig- 
ures of S. cameratus also show the concentric lines. We in- 
cline to believe either that S. cameratus is a mere variety or 
age form of S. striatus or that the synonomy of the two forms 
is inextricably confused. 
