42 
PALEONTOLOGY OF NEW YORK. 
Spirifer without the introduction into that genus of an inconvenient and 
refractory element. The fact of their variation in ornamentation while re¬ 
taining the same contour, prevents the assimilation of the group into any of 
the subdivisions of Spirifer proposed above, and for such a reason it will be 
well to recognize the term, since it has been so long in use. 
Cyrtia is, in effect, a group of cyrtiniform Spirifers, and its specific repre¬ 
sentation is quite small. The type species C. exporrecta, Wahlenberg, occurs in 
the Wenlock limestone, and in the fauna of the Niagara group the same form 
is associated with the variety arrecta, Hall and Whitfield. Mr. Billings’s species 
C. Myrtea, from Division 4 of the Anticosti series, appears to be identical with 
C. exporrecta. These, and a larger form from the Niagara dolomites of Wiscon¬ 
sin, which we shall term C. radians, sp. nov., all have the filamentous surface 
markings which characterize the Silurian Spirifers of the S. radiatus-iypQ, 
though they show no tendency to become plicated. In the Devonian faunas 
the external ornament changes; thus in C. Murchisoniana, the shell is finely 
plicated on the sides and over fold and sinus, as in the Spirifer disjunctus-growp 
of the Ostiolati; in C. cyrtiniformis, Hall and Whitfield, of the upper Devonian 
of Iowa, the plications are coarser and more nearly equal over the lateral and 
median regions; in C. simplex {Spirifer simplex, Phillips), of the middle Devonian 
of Great Britain and Europe, the surface, as usually preserved, is apparently 
smooth, with sometimes traces of a few coarse lateral plications near the mar¬ 
gins. Finely preserved examples of this species from the vicinity of Bredelar, 
Westphalia, show that the surface is covered with closely crowded concentric 
rows of very fine and short, simple spinules, as in the unicispinate group of the 
fimbriate Spirifers. The Spirifer altus. Hall, of the Chemung group, is another 
form which may be referred to Cyrtia. It has the lateral slopes more strongly 
plicated than C. simplex, and traces of plications are also visible upon the fold 
and sinus. It is remarkable for its great size and also for its agreement with 
C. simplex in the peculiar retrorse slope of the cardinal area which throws the 
apex of the pedicle-valve over, or in front of the center of the shell. In the 
Devonian Cyrtias the foramen in the deltidium is frequently obscured or absent 
at maturity. It may have existed at earlier stages of development and have 
