xvi. DIMYARIA. GASTEROPODA. 439 



Lithodomus. sp. U. G. Wanninster. 

 Lucina Dupiniana. 0. G. S. U. G. Devizes. 

 Modiola. sp. U.G. Devizes. L.G. Seend. 

 Myacites mandibula. Sow. U. G. Devizes. 

 Mytilus siliqua. 0. G. 8. U. G. Devizes. 

 Nucula impressa. 0. G. 8. L. G. Devizes. 

 Opis Coquandiana. D'Orb. L. G. Seend. 



neocomiensis. D'Orb. L.G. Seend. 

 Pectunculus. sp. L.G. Faringdon. 



umbonatus. Sow. G. Ridge, Wilts. 

 Pholadomya decussata. Phil. L.C. Pangbourn. 



Mailleana. D'Orb. U.G. Wanninster. 

 Tellina insequalis. Sow. U. G. Devizes. 

 Thetis major. Sow. U. G. Devizes. 



minor. Sow. L. G. Wilts. 

 Trigonia spinosa. Sow. U. G. Devizes. 

 Unicardium Ringmeriense. 0. G. 8. U. G. Devizes. 



This list, probably very incomplete as to species, exhibits a large 

 enough series of genera to justify the remark of the greater affinity 

 of the dimyarian families in the greensand to those of the oolites, 

 than is to be found on comparing the lower and upper parts of 

 the cretaceous system of strata. The reason is obvious the sandy 

 groups of the lower cretaceous rocks were in a considerable degree 

 of littoral origin ; the chalk was formed in deeper and quieter water 

 farther from shore. 



GASTEROPODA. 



Acmaea tenuicosta. U. G. Devizes. 

 Emarginula Guerangeri. D'Orb. L. C. Wilts. 



neocomiensis. D'Orb. L. G. Seend. 

 Natica cretacea. 0. G. S. U. G. Devizes. 



Gentii. Sow. U.G. Devizes. 



nodosa. Gein. L.G. Faringdon. 



Pleurotomaria perspectiva. Mant. L.C. Tetsworth. U. C. Wanninster. 

 Pterocera bicarinata. Desh. U. G. Devizes. 

 Solarium conoideum. Sow. G. Vale of Wardour. 

 Turritella granulata. Sow. U. G. Vale of Wardour, Wanninster. 

 Vermetus. U. G. Wanninster. 



Holostomatous gasteropods of oolitic genera still prevail, and 

 carry on the mesozoic life toward the tertiary period, when the 

 other great group of siphonostomata begins to contend for numerical 

 superiority. 



CEPHALOPODA. 



Ammonites auritus. Sow. U. G. Devizes. 



Bendantii. Brong. G. Vale of Wardour. 



