Pcniiiait J'Isli Mciiaspis. — Dean. 49 
IN THE MATTER OF THE PERMIAN FISH 
MENASPIS. 
By Bashfokd Dean, New York. 
PLATE II. 
Among fossil fishes IMcnaspis has been the source of con- 
siderable discussion. For, while it belongs, generally speak- 
ing, within the interesting circle of the more ancient sharks, 
it shows structures v/hich are so puzzling one does not wonder 
that very discordant views have been held regarding its posi- 
tion in the system of fishes. 
Thus, Ewald early maintained that it was akin to Cepha- 
laspis. Jaekel, on the other hand, contended that it represented 
a "Trachyacanthid," that is, a "placoid" connected with Coch- 
liodus, Oracanthus, Sandalodus. Onchus.* Among other ex- 
perts, A. Smith-Woodward has regarded it as an armored 
shark of "some unknown group," and Reis has placed it near 
the xenacanthids, i.e., ichthyotomous sharks, but later empha- 
sized its chimseroid characters. The discussion, however, has 
subsided during the past decade, and it is pnly in the light of 
an undescribed fossil and after a re-examination of the valu- 
able chimseroid material in the British jNIuscum, and in the 
Palseontological Museum in Jermyn street, that the present 
writer has been led to reopen the question of its relationships. 
Menaspis is remarkable on two main grounds. The head 
region. Fig. lA, is surmounted by what appears to be a series 
of paired spines (some of which are of a kind apparently un- 
known in any fishlike vertebrate) which pass from the region 
of the mouth backward on eithc'r side in a graded series. 
Second, the region which has been regarded as the trunk is en- 
closed in broad, almost plate-like tubercles, of which a posterior 
pair protrudes backward, Fig. lA, C^ suggesting somewhat the 
posterior rim of the shoulder armoring in an Ostracophore. 
These features, it may be remarked, are fully taken into ac- 
count by professor Jaekel in his description (1891) of the im- 
portant example of the fossil noticed by Giebel and Ewald. 
"To .T.apkel. in short, it typifies a stage in tlie phylogeny of fishes where 
(he doDtition was plate-Iike and permanent, and where the dermal armoring 
was gradually becoming reduced in transition from the plated paljpozolc 
fishes to the 'shagreen coaled sliarks He later ('OOi shifts his ground and 
admits that Trachyacanthids may occupy a position intermedi*te between 
sharks and chima}roids. 
