114 PISCES. 



which the premaxilla becomes much extended and partly 

 excludes the maxilla from the oral border, while the parietal 

 bones are separated by the supraoccipital, and the well-ossified 

 otics bulge outwards on either side. 



The Pholidophoridae are provisionally placed here on ac- 

 count of their remarkable resemblance to the Leptolepidas. It 

 is not yet quite clear that the mandible was destitute of splenial 

 and coronoid elements, while the baseosts of the pectoral fin 

 have not hitherto been observed. The external bones, scales, 

 and most of the fin-rays are coated with ganoine, and minute 

 fin-fulcra are observable. The maxilla is loose and bounded 

 above by two supramaxillaries ; the gape of the mouth is wide, 

 and the teeth are minute. The vertebral centra are never 

 more than rings, and there are no intermuscular bones. The 

 dorsal fin is short and single. The scales are ordinarily 

 rhombic, united by a peg-and-socket articulation on the ab- 

 dominal flank, but sometimes very deeply overlapping and 

 with a more or less rounded hinder margin. 



Pholidophorus. Small, gracefully fusiform fishes, covered with rhom- 

 bic scales which are usually thin and deeply overlapping, not much deep- 

 ened on the flank, and partly united by a peg-and-socket articulation. 

 The maxilla is arched so that its oral border is convex, and the cheek- 

 plates are very delicate. The sensory canal exhibits radiating branches 

 on the posterior suborbitals. The opercular apparatus is complete, and 

 there are broad branchiostegal rays; but no gular plate has been ob- 

 served. The fins are small, all fringed with minute fulcra; the dorsal 

 is short-based, in the middle of the back; the caudal is deeply forked. 

 The scales are sometimes smooth, sometimes serrated, and usually elabo- 

 rately pectinated in the latest species. The genus ranges from the Upper 

 Trias or Rhsetic to the Purbeck Beds inclusive, the typical species, Pholi- 

 dophorus bechei, with smooth scales, occurring in the Lower Lias of Lyme 

 Regis. The English Purbeckian species (P. ornatus and P. granulatus) 

 and their equivalents in the Lithographic Stone of Bavaria (P. micronyx 

 and P. macrocephalus), are the most highly ornamented and attain larger 

 dimensions than the earlier forms. 



Thoracopterus. Much like Pholidophorus, but with immensely de- 

 veloped pectoral fins. T. niederristi is the only known species, about 

 0'15 m. in length, from the Upper Trias of Raibl, Carinthia. 



Pleuropholis. Small fishes entirely covered with rhombic ganoid 

 scales, of which one longitudinal series on the flank is excessively 

 deepened. The lateral line is remarkable inasmuch as it does not 



