98 HENRY SHALER WILLIAMS 
a distinction between the Ithaca and Chemung forms going under 
the name, this species cannot be regarded as strictly diagnostic of 
the typical Chemung fauna. 
Nos. 19 and 20, Alrypa spinosa and Atrypa reticularis, are both 
recorded from lower horizons than the Chemung by Hall in the 
Paleontology of New York,* so that they too must be discarded from 
the list as not strictly diagnostic of the fauna. 
DIAGNOSTIC SPECIES OF THE TYPICAL CHEMUNG FAUNA 
Excluding the above mentioned species there are left the following 
eleven species characteristic of the original Chemung group, as 
expressed in the section at Chemung Narrows a few miles west of 
the town of Chemung, viz.: Plerinea chemungensis, Leptodesma 
spinigerum, Leptodesma protextum, Goniophora chemungensis, M yti- 
larca chemungensis, Productella lachrymosa, P. lachrymosa lima, 
Stropheodonta (Douvillina) mucronata (Van.), Dalmanella carinata, 
Dalmanella tioga, Spirijer disjunctus. ‘The question may appro- 
priately be raised what is the known vertical range of these species, 
and how sharply may the Nunda-Chemung boundary be drawn by 
means of their appearance in the rocks ? 
Range oj the species.—The first species, Pterinea chemungensis 
(Conrad), is reported only from this Chemung locality and formation 
in the Paleontology of New York.? In that volume several closely 
allied species are described; in the case of none of the species is a 
locality or range indicated which would exclude them from this 
fauna. The species are Pterinea consimilis Hall, from Bucks quarry 
and Chemung, Chemung County, and Smithboro, Tioga County; 
Pterinea rigida Hall, from several localities in Chemung County; 
Pterinea prora Hall, from Bucks quarry and Chemung upper Nar- 
rows; also Pterinea (Vertumnia) reversa Hall, and Pterinea (Ver- 
tumnia) avis Hall; the subgenus Vertumnia was erected on the 
character of reversal of the characters of the opposite valves of the 
shell so that the right valve of Vertumnia appears like the left valve of 
typical Pterinea The species of Vertumnia are also restricted to the 
horizons through which the normal species range. 
1 Op. cit., Vol. IV, 1867, pp. 321, 325. 
2 Op. cit., Vol. V, 1884, p. 98. 
