BRITISH FOSSILS. 



Decade VI. Plate II. 



PALiEONISCUS EGERTONI. 



[Genus PAL^ONISCUS. Agassiz. Palceothrissum, De Blainville. (Sub-kingdom 

 Vertebrata. Class Pisces. Order Goniolepidoti. Family Lepidostei. Sub-family Lepi- 

 dostei heteroceri. 1st Group. Body fusiform ; dorsal fin single.) Dorsal fin commences 

 opposite the interspace of the ventrals and anal ; pectorals and ventrals small ; large 

 fulcral scales on the anterior margins of the dorsal, anal, and caudal fins ; tail with two 

 lobes; heterocerque.*] 



Synonyms. — Palceoniscus Egertoni, Agassiz, Poiss. Foss., vol. ii. p. 302. 

 Palceoniscus Egertoni, Egerton, Quarterly Journal Geol. Soc, 1849, vol. vi. 

 p. 5. 



Description. — This species belongs to a limited group of Palce- 

 onisci, composed of fishes of small size, remarkable for the large and 

 flowing form of the dorsal and anal fins, resembling in this respect 

 the Amhlypteriy and restricted (as these are) to deposits of the coal- 

 measure period. The species under consideration is one of the 

 smallest of the group, its entire length being not more than 2^ 

 inches. The body is fusiform, its greatest depth being immediately 

 in advance of the dorsal fin, where it measures 7 lines. From this 

 point it contracts gradually anteriorly, but posteriorly the contrac- 

 tion is more rapid to the commencement of the caudal fin. The 

 head is small and slender, occupying less than one fifth of the entire 

 length. The bones are ornamented with strongly-defined sinuous 

 ridges. The characters of the opercular apparatus and the mouth 

 are not shown in the specimen. The pectoral fins are composed of 

 about ten flattened rays. The anterior margin of the fin is provided 

 with a delicate fi:inge of small rays. The other rays have very few 

 transverse sutures, and do not bifurcate imtil near their terminations. 

 The dorsal fin commences a little in advance of the opposite insertion 

 of the anal fin. It contains about 25 rays, of which the four or five 

 anterior ones increase in length in succession from before, forming 

 an ornamental border to the fin. The fifth ray is the longest, the 



[VI. ii.] 



* Poiss. Foss., vol. ii. p. 4. 



