224 Percesoces and Rhegnopteri 



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. 



Crossognathidae. A peculiar primitive group referred by 

 Woodward to the Percesoces is the family of Crossognathida 

 of the Cretaceous period. As in these fishes there are no fin- 

 spines, they may be perhaps better placed with the Haplomi. 

 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, Syll&mus latifrons and other species in 

 the Colorado Cretaceous, and Syllamus anglicus in England. 

 The Crossognathida have probably the lower pharyngeals sep- 

 arate, else they would be placed among the Synentognathi, a 

 group attached by Woodward, not without reason, to the 

 Percesoces. 



Cobitopsidae. Near the Crossognathidcs may be placed the 

 extinct Cobitopsidcs, Cobitopsis acuta being recorded from the 



FIG. 177. Cobitopsis acuta Gervais, restored. Oligocene of Puy-de-D6me. 



(After Woodward.) 



Oligocene of Puy-de-D6me 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 Cobitopsis is 

 uncertain. 



Suborder Rhegnopteri. The threadfins (Polynemidce) 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, 



