ITHACA FAUNA 



447 



, Pelecypocla 



41. Aviculopecten cancellatus Hall 



This may be a derivative of one of the small aviculopectens of 

 the Hamilton, such as A. idas or A. scabridus, with whieli the 

 3^oung of our species agree in form. 



45. Aviculopecten striatus Hall 

 Of Hamilton ancestry. 



47. Conocardium liratum Hall 



Probably derived from C. denticulatam of the Hamilton. 



48. Edmondia suhovata Hall 



The species of Edmondia are all post-Hamilton and are prob- 

 ably immigrants from some western fauna. 



51. Gonioplioi'ci minor Hall 



A small form — undoubtedly derived from a Plamilton species 

 of the genus. 



56. Leptodesma naviforme Hall 



Derived from some Hamilton species of the genus. 



59. Macrodon chemungensis Hall 



Clearly derived from M. Immiltonice, with which the young agree 

 closely. 



61. Microdon (Cypricar delta) gregarius Hall 



This is a modification of M. bellistriatus of the Hamilton. It 

 occurs in the Upper Hamilton and passes into the Ithaca and 

 Chemung. 



65. Modionnorpha neglecta Hall 



Probably derived from M. sid)alata. 



69. Mytilarca umhonata Hall 

 Derivation doubtful. 



7'5. Palceoneilo flexuosa (Conr.) 



A modification of the Hamilton P. constricta. 



