BRITISH FOSSILS. 



3 



only 2 inches from the commencement of the tail. This backward 

 position of the dorsal fin is a feature found in all the Aspidorhynchiy 

 but in the species under description it obtains its maximum eccen- 

 tricity. The scales are for the most part exposed on their under- 

 surface. The principal series, or that traversing the middle of the 

 flank, is composed of scales about half an inch in depth. This is 

 succeeded above and below by several series of much smaller dimen- 

 sions. The substance of all the scales is thinner than in any of the 

 oolitic species, and the articulating rib on the inner face is less 

 prominent. The outer surface of the scales, with the exception of 

 those along the back of the fish, is smooth and devoid of ornament. 

 The dorsal series, however, is characterised by strongly marked 

 crests of enamel, arranged in continuous lines in the longitudinal 

 direction of the scales. These ridges are most prominent in front of 

 the dorsal fin. The tail is slender and deeply forked, forming an 

 appropriate finish to the graceful outlines of this, one of the most 

 elegant denizens of the waters in which it lived. 



Locality. — The Dorchester Museum possesses two specimens of 

 this rare fish, procured by Mr. Wilcox, of Swanage, from the quarries 

 of Purbeck stone in that vicinity. I have named it in compliment 

 to the Eev. Osmund Fisher, owing to whose exertions the town of 

 Dorchester is in possession of a very thriving museum, and through 

 whose kindness I have had the opportunity of examining all the 

 valuable materials in that depository. 



Explanation of Plate. 



Fig. 1. Aspidorhynchus Fisheri, size of nature. 

 Fig. 2. Dorsal scales, magnified. 



P. DE M. Grey Egerton. 



June 1853. 



