102 HENRY SHALER WILLIAMS 
size for the genus and elongate tubercles scattered sparsely over the 
surface, become conspicuous at the horizon where the line between 
Nunda and Chemung is drawn. Nevertheless, specimens occur below 
this line which might be referred to the species, though they do not 
express the dominant characteristics of the species at these lower 
horizons. The dominant forms in the faunules below the line differ 
either in size, and thus become referable to the species P. shumardiana 
or P. spinulicosta; or else differ in the surface markings and fall 
under the definition of P. speciosa in which also the form is less ventri- 
cose and the initial umbonal portion is relatively sharper and nar- 
rower in relation to the full dimensions of the shell. The Chemung 
fauna is therefore characterized by the presence of Productella lach- 
rymosa and its variety P. lima, but on account of the great plasticity 
of the genus, and the fact that the genus is abundantly represented 
in the Brachiopod faunules anywhere above the Genesee as at present 
defined, it cannot be said that the species as defined is strictly diag- 
nostic of a Chemung fauna and horizon. 
Stropheodonta (Douvillina) mucronata (Con.).—This species was 
originally described by Conrad under the name Strophomena mucro- 
naia, from Chemung Narrows, associated with Productella lachry- 
mosa.* It was next referred to by Hall under the name Siro phomena 
interstrialis. Hall regarded it at that time as identical with Phillips’ 
species of that name.’ Later Hall described the same species as a 
new species under the name Stropheodonta cayuta,3 applying the 
name proposed by Conrad to the form occurring abundantly at Ithaca 
which had been already well figured by Vanuxem4 under the name 
Sirophomena interstrialis. Wall thus confused under the specific 
name mucronata, both species which he distinguished in the separa- 
tion of the original figures in his report as 5 and sa from 50 and 50, 
referring the latter two, which present the typical character of Con- 
rad’s description to a new specific name Stropheodonta cayuta, and 
applying Conrad’s name to the first two of the set which do not offer 
the distinctive characteristics of Conrad’s description. The result, 
t Conrad, Jour. Acad. Nat. Sci. (1842), p. 257, Pl. 14, Fig. 10. 
2 Hall, Geol. Fourth Dist. N. Y. (1843), p. 266, Fig. 5. 
3 Hall, Paleography of New York, Vol. V (1867), p. 110. 
+ Vanuxemi, Geol. N. Y. Rept. Fourth Dist. (1842), p. 174. 
