PALAEONTOLOGY OF THE LIAS. 71 



Walcottii ; and, although so numerous, the species appears 

 to have found its last resting place in these beds, as it lias 

 never been found in those of a later age. The class 

 Brachiopoda, animals having long extensile arms, to which 

 the Spirifer and Terebratula belong, are numerously re- 

 presented. 



The State in which some of the Spirifers are found, has 

 enabled dissections to be made of their interiors ; and an 

 enlarged sketch of the remarkable structure they present, 

 may be seen in the volume of the Palasontographical 

 Society for 1850. Having paid raore than ordinary atten- 

 tion to Shells of this family, I have been able to add ma- 

 terially to known forms. 



Until lately, only fourteen species belonging to the 

 genera Lingula, Orbicula, Spirifer, and Terebratula, were 

 published, from all the Lias beds of this country. Three 

 new o-enera, viz : LeptcBna, Thecidea, and Crania, including 

 in the whole nineteeu species, have since been figured and 

 described by my friend Mr. Davidson, in the last year's 

 volume of the Palfeontographical Society, from my collec- 

 tion, since w^hich I have discovered about ten others, 

 thereby increasing the species in this family, from the Lias 

 from fourteen to forty-three. 



The Leptcence vrere supposed to have become extinct at 

 the termination of the Palteozoic period; but as five or 

 more species existed at the time of the deposition of the 

 Upper Lias, this was not the case, but they have become 

 much degenerated in size, one species, the LeptcFna Bou- 

 chardii, not being much larger than the head of a good 

 sized pin. These shells are found in the beds of clay in- 

 tervening between the Maristone and the fish bed. They 

 seem to have been deposited very slowly; and although 

 they are of inconsiderable thickness (in the whole but 



