STREPTORHYNCHUS. 
©7 
the general form, and the alternation of coarser and finer stria©, corre¬ 
spond very nearly with the specimens in the Chemung group of New- 
York ; and with the materials before me, I can find no specific distinc¬ 
tion. 
The variety of forms heretofore described as species have been studied 
at different times and under different circumstances; and it has only 
been after the entire series from the successive formations were brought 
together, with large accessions of individuals, that their true relations 
could be established. 
Two other species of Streptorhynchus have been described from the sandstone 
of Burlington, Iowa. One of these, in a single specimen examined, presents some 
marked differences; but having no extensive collections from that place for com¬ 
parison, I do not know what variation either of them may present on farther 
examination. 
Streptorhynchus cliemungensis. 
PLATES IY, IX & X. 
Strophomena chemungensis : Conrad, Jour. Acad. Nat. Sciences, Vol, viii, pa. 357; pi. 14, f. 12. 1843. 
Strophomena bifurcata : Hall, Geol. Rep. 4th Dist. New-York, p.266, f. 2. 1843. 
Strophomena arctostriata : Hall, Ibidem, p.266, f.3. 1842. 
Strophomena pectinacea : Hall, Ibidem, p. 266, f. 4. 1842. 
Orthis perversa : Hall, Tenth Report on the State Cabinet, p. 97. 1847. 
Streptorhynchus pandora : Billings, Canadian Journal, [N.S.], No.xxvii, p.226. 1860. 
«< “ Billings, Geology of Canada, p.369. 1863. 
Orthisina arctostriata : Hall, Thirteenth Report on the State Cabinet, p. 80. 1860. 
Orthisina alternata : Hall, Ibidem, p. 81. 1860. 
Orthis inequalis and Orthis pfavus : Hall, Geol. Report of Iowa, Part ii, pa. 49, pi. 2, f. 6. 
The following is the description of the species given by Mr. Conrad : 
“ Semiorbicular. Inferior valve ventricose : superior valve slightly con- 
“ cave, with a prominent umbo; radii very numerous, prominent, sub- 
“ equal; umbo of inferior valve ventricose, summit not prominent; 
“ hinge-angles nearly rectangular; margins extending in a very regular 
“ curve from the cardinal extremities. 
“ Locality : Chemung-narrows, New-York. Devonian.” 
This description is applicable to many of the specimens of the Chemung group, 
but the figure given is proportionally longer than those among my collections. 
There is, however, no other species in the Chemung group to which the description 
applies. 
