in relation to the dorsal margin of the body. The last ray has no corre- 

 sponding interneuralium. 



The anal fin. The rays here, some 13 — 14 in number, are thinner 

 than those in the dorsal fin; the first two extremely short, similarly 

 as in Idrissia juhae. The interhaemalia thin, about 11 — 12 in number, 

 absent in the first and last rays. The best preserved anal fins are on 

 specimen 164 Os. (holotype), 77 Os. (paratype) and 87 Os. The base of 

 that fin corresponds to the length of 6 — 7 caudal vertebrae. Its beginning 

 occurs far behind the dorsal fin, below the 13th — 14th vertebra (from 

 the back). The distance between the last ray of the dorsal fin and the 

 first ray of the anal fin corresponds to the length of 8 — 9 precaudals. 

 The preanal area represents 76 — 81 percent of the body length without 

 the caudal fin. The narrow alimentary canal terminates just before the 

 anal fin; in all the specimens available it is well preserved as a black 

 organic substance. 



The caudal fin. Strongly notched, consisting of 11 strong cardinal 

 rays and 10 short side rays (in each lobe), most satisfactorily preserved 

 on specimens Nos. 164. Os. (holotype) and 87. Os. The length of the 

 longest rays represents about 20 percent of the body length without the 

 caudal fin. 



The whole body was covered by scales the traces of which have 

 persisted only as faintly indicated impressions. Some of the specimens 

 bear pigment spots, as a rule restricted to the upper half of the body; 

 just a few may occur ventrally near to the base of the caudal fin. 



General remarks. A comparative study of the species described 

 above with the fossil representatives of Gonostomidae, previously re- 

 corded, justifies its assignment to the genus Idrissia Aramb., described 

 from the Upper Cretaceous of North Africa (Arambourg, 1954). Until 

 now, this was a monotypic genus, represented by Idrissia juhae Aramb. 

 The differences between the two species are shown in Table 2. 



According to Arambourg (1954), the beginning of the development 

 of the Gonostomidae occurred during the Cretaceous, since the oldest 

 thus far known representatives of this family are the Cretaceous 

 genera Idrissia Aramb. and Paravinciguerria Aramb. Arambourg sup- 

 poses that they represent extremely primitive forms; in spite of the lack 

 of photophores, he connects Paravinciguerria Aramb. with the living 

 genus Vinciguerria Goode and Bean. The fossil remains of the latter, 

 with photophores preserved, are known as early as from the Oligocene 

 (Danilchenko, 1946). 



In arrangement of fins and number of rays on the dorsal and 

 anal fins, the living genus Ichthyococcus Bonaparte from the Gonosto- 

 midae seems to approach Idrissia Aramb., another of the most ancient 



2* 11 



