44 INTRODUCTION. 



Cydas membranacea. Sow. M. C. t. 527. 

 Neritina Fittonii. Sow. G. T. iv. t. 22. f. 7. 

 Paludina Sussexensis. Sow. G. T. iv. t. 22. f. 6. 

 Melanopsis ! tricar inata. Sow. G. T iv. t. 22. f. 4. 



? "attenuata. Sow. G. T. iv. t. 22. f. 5. 



Cydas parva. Sow. G. T. iv. t. 22. f. 7. 



subquadrata. Sow. G. T. iv. t. 21. f. 8. 



elongata. Sow. G. T. iv. t. 21. f. 9. 

 angulata. Sow. G. T. iv. t. 21. f. 12. 



major. Sow. G. T. iv. t. 21. f. 13. 

 In Wealden clay. 



Unio porrectus. Sow. M. C. t. 594. f. 1. 



compressus. Sow. M. C. t. 594. f. 12. 



ambiguus. Sow. M. C. t. 594. f. 3 5. 



aduncus. Sow. M. C. t. 595. f. 2. 



cordiferus. Sow. M. C. t. 592. f. 1. 



In sandstone of Tilgate forest. 



There are some other Paludince, Uniones, *c., figured 

 in Mr. Sowerby's Mineral Conchology, but they appear 

 to be properly referrible to the marine genera, as 

 they are found with decidedly marine shells. It 

 should be remarked, that all the recent species of 

 Melania^ Melanopsis, and Potamides are confined to 

 the warmer and nearly tropical parts of the world. 

 A small species of Melania (M. helvetica) only has 

 been found in the south of Europe ; and there is a 

 larger species (Melania Virginica) found in North 

 America. 



The situations chosen by the different species of 

 land shells, are characteristic, and worthy of ob- 

 servation. Thus 



Helix Pomatia is found on the ground. It buries 



