STKEPTORHYNCHUS. Sy 



the general form, and the alternation of coarser and finer striae, 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 cheI^^ngensis. 



PLATES IV, IX & X. 



Stropkomena chemungensU .• Conrad, Jour. Acad. Nat. Sciences, Vol, viii, pa. 357; pi. 14, f. 12. 1848. 



SiTophomtna bifurcata : Hall, Geol. Kep. 4th Dist. New- York, p. 266, f.2. 1843. 



Stropkomena arctottriata : Hall, Ibidem,' p. 266, f. 3. 1842. 



Stropkomena pectinacea : Hall, Ibidem, p. 266, f. 4. 1842. 



Ortkit perverta : Hall, Tenth Report on the State Cabinet, p. 87. 1847. 



Strtptorkynckut pandora : Billisos, Canadian Journal, [N.S.], No.xxvii, p. 226. 1860. 



<< •• BiLLisos, Geology of Canada, p. 369. 1863. 



OrikUina arctottriata : Hall, Thirteenth Report on the State Cabinet, p. 80. 1860. 

 OrtkUina alternata : Hall, Ibidem, p. 81. 1860. 

 Ortkit inequalit and Ortku pravut : 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, eub- 

 " 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. 



