58 C0NTKII3UTI0NS TO DEVONIAN PALEONTOLOGY. [bull. 244. 
has come to the conclusion that this species does not occur in the New 
York sections until the Chemung fauna enters that province, thus mark- 
ing' the transition between the Nunda (Portage) formation a and the 
Chemung. This conclusion, which is founded on evidence furnished 
by numerous sections exhibiting continuous strata across the transi- 
tion, causes the Erie shale of Lero}% Ohio, to be assigned to a horizon 
as high as the Chemung of New York, rather than in the Nunda 
(Portage). No trace of this species has been reported, so far as the 
writer is aware, from the Ithaca member or any equivalent horizon. 
Hence the species may be regarded as diagnostic of the Chemung 
formation, and not of the Nunda (Portage). 
Delthyris mesicostalis is quoted by Schuchert as appearing in c ' Ithaca 
and Chemung (Dev.)." 6 If it be assumed that Spirifer pennatus 
Conrad var. posterus, H. & C. c and Delthyris mesicostalis Hall^ are 
generically distinct they may be distinguished by the absence or very 
rudimentary condition of the median septum in the ventral valve of 
Spirifer pennatus var. posterus and its distinct development in 
Delthyris mesicostalis. If this is used as a distinguishing feature for 
specimens which are very similar in most other characters, it has been 
ascertained by the writer and those associated with him in Devonian 
studies that the specimens occurring at the horizon called the Ithaca 
member in central New York, and in all other regions where it is dis- 
tinctly traced, belong to the form described as Spirifer pennatus 
var. poster as, and that specimens with a distinct septum do not appear 
in the sections until the incoming of the Chemung fauna above the 
Nunda (Portage) formation. Hence the species described as Delthyris 
mesicostalis Hall should be quoted as a diagnostic Chemung species, 
and as not occurring in the Ithaca member. e 
a See footnote, p. 86. d Geol. New York, Rept. Fourth Disk, 1843, p. 269. 
b Bull. U. S. Geol. Survey No. 87, p. 207. eSee further notes on pp. 75, 76, 108. 
c Pal. New York, Vol. VIII, Pt. II, p. 361. 
