26 
MESOZOIC VERTEBEATA. 
4—DESCRIPTIONS OF MESOZOIC VERTEBEATA. 
PISCES. , ' . 
?PBROBSOCES. 
SYLLiBMES, Cope. 
Report U. S. Geol. Surv. Terrs., ii, p. 180. 
Allied to the Mugilidce. A short, spinous dorsal fin; ventral fins ab¬ 
dominal, posterior to the spinous dorsal. Pectoral fins subinferior in posi¬ 
tion. Coracoid bones forming a compressed, keeled body. Scales large, 
cycloid; lateral line present, extending along the middle of the sides. Pa¬ 
rietal bones less than epiotics, entirely separated by the supraoccipital. 
Frontal bones large, wide, their common suture distinct. 
The opercular apparatus extends obliquely backward, while the man¬ 
dible is produced forward. Hence the inferior part of the hyomandibular 
and the symplectic are directed obliquely forward. The end of the muzzle 
is broken off, but the posterior part of the dentary bone does not exhibit 
any teeth. The opercular bones are thin, and their inferior borders reach 
the median line of the inferior side of the head. 
The only species of this genus which has fallen under my observation 
is represented by a specimen in which the body posterior to the femoral 
bones is wanting, ddie surface is covered with scales, so that only the out¬ 
lines of those bones can be distinctly seen. They are thickened, and 
curved outward; those of opposite sides are well separated from each other. 
The scales exhibit a very delicate concentric line-sculpture. 
The very posterior position of the ventral fins distinguishes this genus 
from Mugil, while the inferior position of the pectoral fins is not seen in 
Atherina. The lateral line does not occupy the inferior position seen in the 
Scombresocidee. As compared with Apsopelix, Cope, from the Benton group 
of Kansas, Syllcemus differs in the absence of dorsal radii or interneural 
spines anterior to the ventral fins. There is doubtless some affinity between 
the two genera, as the other characters are quite similar. I was unable to 
detect a lateral line in Apsopelix. It is possible that a catalogue-name of 
Agassiz, viz, Calamopleurus (Poiss. Foss., v, p. 122), refers to this or some 
allied genus; but I am unable to discover that it has ever been described. 
