﻿MTLOSTOMATID^!. 315 



Newberry, op. cit. pi. xvii. fig. 2) more closely resembles that of 

 certaiu species of Coccosteus (e. g. C. disjectus, p. 292) than the 

 corresponding plate of the Asterolepidae ; and the recent description 

 of the complete ventral shield by Claypole (Amer. Geologist, 1890, 

 p. 255, with fig.) proves that it agrees with that of Coccostetis in 

 every essential particular. The " post-dorso-median " plate of 

 Claypole is obviously the anterior median ventral, while the "post- 

 dorso-lateral " and " dorso-lateral " of the same author are the 

 anterior and posterior ventro-lateral plates respectively. 



There are no examples of this genus in the Collection, and only a 

 single species has as yet been recognized, thus : — 



Holonema rugosum, J. S. Newberry, op. cit. p. 93, pi. xvii. figs. 1-4 : 

 Pterichthys (?) rugosus, E. W. Claypole, Prod Amer. Phil. 

 Soc. vol. xx. (1883), p. 666, with fig. : Pterichthys (Bothrio- 

 lepis) rugosus or Holonema rugosum,- E. W. Claypole, 

 Amer. Geologist, 1 890, p. 257, with fig. — Chemung Group 

 (Upper Devonian) ; New Jersey and N. Pennsylvania. 

 Catskill Group (Upper Devonian); New York State. 

 [Median ventral plate ; Museum of Akron College, Ohio.] 



So far as can be determined from the description and imperfect 

 figures, the dermal plates from the Devonian of the Eifel, named 

 Coccosteus obtusus, Koenen (see p. 294), exhibit much resemblance 

 to those of Holonema. 



Family MYLOSTOMATID.E. 



An imperfectly known family, as yet incompletely definable. 

 Dentition consisting of a paired series of few large, dense, tritu- 

 rating plates in each jaw. 



Genus MYLOSTOMA, Newberry. 

 [Trans. New York Acad. Sci. vol. ii. 1883, p. 145.] 



The type genus, known only by the teeth and the bones of the 

 mandible. Principal dental plates triangular or spatulate in form, 

 flattened or with an irregularly tumid coronal surface, which is 

 more or less nearly parallel with the attached surface. Dentigerous 

 bone of the lower jaw exhibiting a much-expanded oral border for 

 the support of the teeth. 



This genus is not represented in the Collection, and has only been 



