1910.] NATURAL SCIENCES OF PHILADELPHIA. 657 



from the rock in place and one from a drift boulder, no other specimens 

 have until recently come to the attention of the writer. It is to 

 Mr. Wheelock that we are again indebted for the discovery of addi- 

 tional and better preserved material. This latter, together with two 

 of the Manlius specimens, allow of the determination of one genus, 

 Machcer acanthus, with certainty, and it is believed that characters 

 differing from those of previously described species indicate that the 

 form in question is new. It is not, however, thought advisable to 

 introduce a new specific name, for it is possible that the features 

 observed may be merely the result of individual variation in some long- 

 known species of the genus. 



Fig. 1. — A and B, proximal cross sections, and C, distal cross section of Machmra- 

 canthus spines from the Oriskany sandstone of Onondaga County, New York. 

 B and C are sections of the same spine. All are enlarged twice. 



The Oriskany Ma cheer acanthus may be briefly described as follows : 

 Spines having a measured width of 16.5 mm. Length probably 

 exceeding 100 mm. This would lie a spine of about the size of 

 M. peracutus Newb. and M. sulcatus Newb., but much smaller than 

 M . major Newb. The angle of convergence of the sides of the spine 

 is less than in any of the above-mentioned species, one measurement 

 showing that the width decreases from 10 mm. to 3 mm. through a 

 length of 54 mm. The curvature is apparently about the same as 

 that met with in M. peracutus. Central cavity large. The cross 

 section of the spine is highly characteristic and changes greatly in its 

 outline distally. In the more proximal portions the spine is marked 

 by very sharp "wings" and an angulated ridge is present on the 

 outer (?) side while the inner (?) carries a much rounded and swollen 

 ridge. Distally the "wings" are shorter, while the two ridges, though 

 still maintaining their general character, become less pronounced. 

 External surface punctate with distally convergent stria?. 



These Oriskany specimens are distinguished from those previously 

 described by the cross section. In this feature they most resemble 

 M . longoevus Eastman 3 from the New York Hamilton, while in general 



3 New York State Museum Memoir 10, p. 85, pi. 2, fig. S. 



