Percesoces and Rhegnopteri 439 
them with the Percesoces, but more recently suggests their re- 
lationship with the Haplomi. Perhaps, as supposed by Gill, 
they may prove to be degenerate berycoids in which the ven- 
tral fins have lost their normal connection. 
Crossognathide.— A peculiar primitive group referred by 
Woodward to the Percesoces is the family of Crossognathide 
of the Cretaceous period. As in these fishes there are no fin- 
spines, they may be perhaps better placed with the Haplomz. 
The dorsal fin is long, without distinct spines, and the abdom- 
inal ventrals have six to eight rays. The mouth is small, 
with feeble teeth, and the body is elongate and compressed. 
Crossognathus sabandianum occurs in the Cretaceous of Switzer- 
land and Germany, Syllemus latifrons and other species in 
the Colorado Cretaceous, and Syllemus anglicus in England. 
The Crossognathide have probably the lower pharyngeals sep- 
arate, else they would be placed among the Synentognatht, a 
group attached by Woodward, not without reason, to the 
Percesoces. 
Cobitopside.—Near the Crossognatlide may be placed the 
extinct Cobitopside, Cobitopsis acuia being recorded from the 
Fic. 346.—Cobitopsis acuta Gervais, restored. Oligocene of Puy-de-Déme. 
(After Woodward.) 
Oligocene of Puy-de-Déme in France. In this species there 
is a short dorsal fin of about seventeen rays, no teeth, and 
the well-developed ventral fins are not far in front of the anal. 
This little fish bears a strong resemblance to Ammodytes, but 
the affinities of the latter genus are certainly with the 
ophidioid fishes, while the real relationship of Cobztopsis is 
uncertain. 
Suborder Rhegnopterii—The threadfins (Polynemide) are al- 
lied to the mullets, but differ from them and from all other 
fishes in the structure of the pectoral fin and its basal bones, 
or actinosts. 
The pectoral fin is divided into two parts, the lower com- 
posed of free or separate rays very slender and thread-like, 
