BRITISH FOSSILS. 



Decade YI. Plate IX. 



LEPTOLEPIS CONSTRICTUS. 



[Genus LEPTOLEPIS. Agassiz. (Sub-kingdom Vertebrata. Class Pisces. Order 

 Goniolepidoti. Family Sauroidei. Sub-family Sauroidei homocerci. 1st Group. Tail 

 forked.) Scales very thin and rounded ; dorsal fin opposite the ventrals ; operculum 

 broad ; sub-operculum large ; teeth villiform ; lower maxillaries with strong coronoid 

 processes.] 



Leptolepis constrictus, Egerton. 



Description. — The genus Leptolepis contains no fishes of mag- 

 nitude, nevertheless, as some of the species are very minute, 

 the range of size is considerable. Leptolepis constrictus holds an 

 intermediate position in this respect. The largest of four specimens, 

 which I have examined, measures 3^ inches from the extremity of 

 the nose to the fork of the tail. The head is small, occupying less 

 than one fourth of the entire length, and of elegant form. Indeed, 

 the whole fish is remarkable for the graceful proportions it displays. 

 The bones of the head are exceedingly thin, and quite smooth, with 

 the exception of the preoperculum, which is characterized by a fan- 

 like group of prominent ridges, radiating from the anterior angle of 

 the bone. This structure distinguishes the species very neatly from 

 Leptolepis concentricus* which has the preoperculum as smooth as 

 the other cranial bones. The mouth is small, and opens upwards. 

 The lower jaws are curved. No teeth are visible in the specimens 

 I have seen, which, in other respects, are in a good state of pre- 

 servation. The coracoid bone is strong and rounded. The spinal 

 column consists of 38 vertebrae. These are longer than broad, and 

 are remarkable for the depth of the constriction of the centrum 

 between the articulations. Hence the specific designation. This 

 constriction gives to each vertebra the form of an hour-glass. The 

 relative position, size, and character of the fins in this genus vary 

 little. In the species under consideration they are all small, and 

 the rays slender. The pectorals contain about 19 rays in each fin, 



* Egerton, Journal of Geol. Soc., vol. v. p. 35. 

 [VL ix.] 6 K 



