264 NEW YORK STATE MUSEUM 



on the field (Hamilton). A. b o y d i, by loss of race force, breaks up at 

 the close of Hamilton time into a number of diminutive and shortlived 

 survivors (A. perstrialis, delta, epsilon, eta, etc.), and to this 

 highly variant superstitial group this shell, A. sola, seems to appertain. 

 It seems out of place, out of harmony with its usual surroundings in asso- 

 ciation with Pterochaenia cashaquae, Ontario accincta, 

 Probeloceras lutheri, etc., and has evidently strayed far. 



LEPTODESMA Hall. I 883 



Leptodesma sp. cf. rogersi Hall 



Specimens of this genus have been occasionally found in the darker 

 shales of the lower part of the Naples beds, and these have somewhat the 

 expression of L. rogersi of the Ithaca fauna. The material however is 

 not sufficient to justify more precise determination. 



Habitat. Genesee province ; Naples subprovince. Parrish gully, 



Naples. 



posidonia Bronn. 1828 



There is a small group of diminutive, thin shelled Devonic and even 

 Siluric shells clearly showing aviculoid characters in the development of 

 the byssal groove and auricle, which are still allowed to pass current under 

 the name Posidonia. The term is, in view of its original application to a 

 Culm species of subcircular form, undeveloped ear and wing and consider- 

 able size, probably inexact in this connection, but it is convenient for con- 

 tinued provisional employment till the distinctive features of the shells 

 have been more fully analyzed. In European faunas such shells have 

 long been noticed in Precarbonic rocks: P. glabra (Miinst.) Barr., 

 Etage E, P. h i a n s Waldschmidt of the Middle and Lower Devonic, 

 P. venusta Miinster, Upper Devonic. Freeh has redescribed and illus- 

 trated these species with a number of others ' employing the term as a con- 

 venience and incidentally suggesting the uselessness of replacing the name 

 Posidonia for the substitutes proposed for it on account of prior occupancy. 



'Die devonischen Aviculiden Deutschlands. 1891. p. 68 et seq., pi. 14. 



