2 



BRITISH FOSSILS. 



is, I think, corroborated by the general form of the mouth, which I 

 now proceed to describe. This organ is entirely bounded by the 

 premaxillary (figs. 1, 2, 6.) and lower maxillary bones. The former 

 are very long, reaching, when the mouth is shut, as far back as the 

 orbit ; they are scimitar-shaped, the curve being backwards and 

 upwards. The lower maxillaries are remarkable for having, at one 

 third distance from the symphisis, a strong ascending coronoid pro- 

 cess (figs. 1, 2, 3, a.) expanded at its upper extremity, and rising 

 nearly at right angles from the dentary bone. In front of this 

 process the bone is thickened out into a table, corresponding with a 

 similar thickening of the proximal ends of the premaxillaries, and 

 well adapted for the support of a cushion of minute villiform teeth. 

 When the mouth is slightly open, the gape is defined by the anterior 

 part of the premaxillaries, and that portion of the lower maxillary 

 in advance of the coronoid process, and is nearly vertical ; but when 

 fully expanded the long premaxillary bones sweep forwards as far 

 as the sympliisis of the lower jaw, carrying with them a broad 

 fold of integument, and forming a cavity nearly equal to the dia- 

 meter of the entire head. The great length of the lower jaw behind 

 the coronoid process provides the means for this enormous expansion 

 of the oral orifice. This singular conformation of the lower jaw oc- 

 curs in the Carps and some of the allied Cycloid fishes of the present 

 day. That Agassiz is correct in arranging Leptolepis in the Sauroid 

 rather than the Lepidoid family, I have little doubt ; for on com- 

 paring it with other genera, I find that the alhed genus Thrissops 

 has also a coronoid process, though of smaller dimensions, with distinct 

 Sauroid teeth, while the genus Pholidophorus, which is liable to be 

 confiised with Leptolepis, has the lower jaw of a very distinct form. 



Description. — This species of Leptolepis is the most slender and 

 elegant of the genus ; the head partakes of the graceful character 

 of the general form, being narrovf and elongated. Its component 

 bones are thin and perfectly smooth, with the exception of the pre- 

 operculum, which is characterized by coarse striations, radiating from 

 its anterior margin. The orbit is large, but not so large (compared 

 with other species) as I conceived to be the case when I gave the 

 name to the species. The spinal column contains about 40 vertebrae ; 

 the terminal ones decrease rapidly in size, and trend slightly upwards. 

 The ribs and the other vertebral apophyses are slender. The pectoral 

 fins contain about 1 2 rays. The ventral fins are situated nearly in the 

 centre of the body, and are comparatively large, containing each 

 from 10 to 12 rays. The dorsal fin is small, and is directly above 

 the ventrals. The anal fin is also small, and placed about mid-way 



