32 
PALEONTOLOGY OF NEW YORK. 
With the increase of the Aperturati, the Ostiolati diminish rapidly and in 
the upper Devonian faunas we know but a single species, (Sf. asper, from the 
Chemung group of New York.* 
VI. Glabrati. Typical examples, Spirifer glaber, Martin, Martiniopsis injiata, 
Waagen. 
Forms with the surface smooth and glabrous; fold and sinus faintly devel¬ 
oped except at the anterior margins of the valves. 
The species embraced in this division have stronger differential characters 
than are found among the preceding groups. The shells have a very short 
hinge and low cardinal area, and the subcircular marginal outline causes a 
noticeable alteration in the form of the spiral arms. These have their bases 
well forward and are extended obliquely to the rounded cardinal extremities, 
in their position thus approximating the form assumed by these organs in 
Cyrtia and Cyrtina ; the crura, also, and the primary lamellae become very 
long. This difference is not, however, one of great significance and is to be 
expected in any Spirifer having such an outline. 
The character of the muscular impressions is of greater importance; the 
broad scars of the diductors in the pedicle-valve are here reduced to very 
narrow dimensions, are scarcely depressed and frequently not defined, but 
represented only by a radiate marking of the shell. In the brachial valve the 
adductor scars are two narrow impressions which widen anteriorly but are not 
divided transversely. The surface of the shell was covered with very fine 
concentric lines and the epidermal layer which is usually effaced, was minutely 
punctate. Faint lateral plications are sometimes visible. 
These difierences from the normal type of Spirifer have led many writers 
to adopt McCoy’s term Martinia for S. glaber and its allies. It is evident, 
however, that this division of the smooth-shelled species embraces more than 
one subordinate type of structure; they may divided into 
I. Aseptati (= Martinia, McCoy, 1844). Shells in which dental lamellae and 
septa are wanting. 
* Thei-e is a large and hitherto undescrilied representative of this group in the limestone at Littleton, 
Iowa, which is 7-egai-ded By Pi ofessor Calvin as of upper Devonian age. 
