BRITISH FOSSILS. 



Decade VI. Plate IV. 



PHOLIDOPHORUS PACHYSOMUS. 



[Genus PHOLIDOPHORUS. Agassiz. (Sub-kingdom Vertebrata. Class Pisces. 

 Order Goniolepidoti. Family Lepidostei. Sub-family Lepidostei homocerci. 2d Group, 

 Body elongated, more or less fusiform.) Dorsal fin small, opposite the ventrals ; caudal 

 fin forked ; the lobes equal ; the base of the upper lobe invested with scales ; teeth 

 villiform.*] 



Pholidophorus pachysomus^ Egerton. 



Description. — This species is easily detected by its stumpy and 

 inelegant proportions, which contrast strongly with the graceful 

 forms of the associated Pholidophori. The head bears the propor- 

 tion of 2 to 7, as compared with the length of the fish to the inser- 

 tion of the caudal fin, whereas this measurement in Pholidop)horus 

 Bechei is as 1 to 4. The depth of the body at the dorsal fin is 

 equal to one half of the length from the scapular arch to the tail. 

 This unusual proportion gives an oval outline to the body, very 

 distinct from the fusiform shape of the generality of the species. 

 As compared with Pholidophorus Bechei the lower jaw is shorter 

 and stronger, the orbit larger, and the surface of the opercular 

 bones less uneven. The rays composing the pectoral fin are more 

 slender. The space from the occiput to the insertion of the dorsal 

 fiiJi^is much less, as is likewise the distance between the ventral 

 fins and the tail. The other characters of the natatory organs 

 correspond pretty nearly with those of that species. The scales 

 are of large size, and perfectly smooth. The series, counting along 

 the lateral line from the scapular arch to the tail, contain only 

 80 scales, being 10 less than are found in Pholidophorus Bechei. 

 Those in the centre of the flanks are the largest. The posterior 

 edges are curvilinear, and slope rather obhquely backwards and 

 downwards ; in some specimens they are translucent, in consequence 

 of the thin plate of ganoine projecting beyond the opaque material 



[vi. iv.] 



* Poiss. Foss., vol. ii. p. 9. 



