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- " ' MYLOSTOMATIDjE, . ^ ^ 315 
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Newberry, 07 ?. ciY pi. xvii. fig. 2 ) more closely resembles that of 
certain species of Coccostens (e. g. (7. clisjeclus , 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 Coccosteus in 
every essential particular. The “ post-dorso-median ” plate of 
Claypole is obviously the anterior median ventral, while the “ post- 
dorso-lateral v 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. ng a . 1-4: 
Pterichthys (?) rugosus , E. W. Claypole, Proc. Amer. Phil. 
Soc. vol. xx. (1883), p. 666 , with fig.: Pterichthys ( Bothrio- 
lepis) rugosus or Holonema rugosum , E. W. Claypole, 
Amer. Geologist, 1890, p. 257, with fig.—Chemung Group 
(Epper Devonian); New Jersey and N. Pennsylvania. 
Catskill Group (Upper Devonian); New York State. 
[Median ventral plate ; Museum of Akron College, Ohio.] 
ff- H- r u ^e~>u ^ t d- PPr ), Afirfo, fS 2 *t <■ /? S Ev hn^'c. <rtv s.) ku < fo f <?y. tf-Oe^m- 
So far as can be determined from the description and imperfect 1 ' 
figures, the dermal plates from the Devonian of the Eifel, named 
Coccosteus obtusus, Koenen (see p. 294), exhibit much resemblance 
to those of Holonema. 
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Family MYLOSTOMATIDiB. 
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 MYLOSTOBTA* 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 
