ITHACA FAUNA 



443 



44. Aviculopecten rugcestriatus Hall 



Undoubtedly derived from Hamilton species of the genus, of 

 which there are several rather closely related ones. 



49. Glossites depressus Hall 



I^ot unlike the Hamilton G. siih tenuis from which it may be 

 derived. 



52. Grammy sia siibarcuata Hall 



This seems to be a derivative of the Hamilton G. arcuata, with 

 which the young agrees. In the adult it is more elongate and has 

 a more pronounced cincture than the Hamilton species. 



53. Leda (Nuculana) curta Meek 



This was described from the Saint Louis limestone. It is prob- 

 ably a mistaken identification. 



57. Leptodesma sociale Hall 



This might readily be a modification of L. rogersi of the 

 Hamilton. 



67. Modiomorpha suhalata var. chemungensis Hall 



This is a modification of the characteristic species of the 

 Hamilton group. The main change is in proportion, the variety 

 being larger. 



68. Mytilarca chemungensis Conrad 



The derivation of this form is not clear. 

 71. Nucula diffidens Hall 



This appears to be derived from Nucula yandelH of the Ham- 

 ilton, which the young stages suggest. 



77. Pakroneilo filosa (Conrad) 



Allied to P. fecunda of the Hamilton group, from wliicli it ap- 

 parently is derived. 



87. Pterochcenia fragilis Hall 



This is an immigrant from the Naples fauna in the western 

 part of the State. 



91. Spatliella typica Hall 



The derivation of tlie form is doubtful. 



