'DA. 

 Ortborvn* oolalr.) 



intcniipt the -iirfare sculptim-. luit liav> the appearance of opaque or dull li 

 upon the -hilling surface of the -lull. These I pro-nine to be traces of color line- 



Formation ami /...-n/i'/y.- -In tin- Trvnton limestone, Cannon Kill)-. Minnesota. G'll.-i-ii..n of \V II 



ORTHOCKRAS SOCIAL*: Hull. 1877. 



I'LATK LV. FIG. T. 



Orthoetrai grtgarium HALL, 1MI. lU-pt. Supt. Ool. Surv. Wisconsin. p. 46. 



OrtHoftrat *. i - II M i 1ST*. In Miller's North American Palaeozoic KoMlls, 2rt <!., p. . 



description: "Shell of medium >i/.e, gradually expanding from the 

 apex. transverse section circular. Septa deeply concave, not very distant, varying 

 from six to nine in the space of an inch, according to age. Siphuncle central in 

 young specimens, often becoming subcentral or quite excentric in old individuals." 

 This species which is better known from the general diffusion in collections of 

 the fine specimens occurring in rocks of the Hudson River horizon in the Maquoketa 

 region of Iowa than from any published accounts or illustration, is represented in 

 the collections of the Minnesota survey by excellent representatives from Graf, 

 Iowa. There are also a few examples from the Trenton and Qalena horizons at 

 Cannon Falls which l>ear very much the same proportions, symmetrical form and 

 general aspect of 0. sociale and hence suggest the presence of that species in these 



rocks. 







ORTHOOERAS BKLTRAMII, sp. nov. 

 PLATE LV. no. 10. 



Shell very small, straight, very gradually expanding; cross-section subelliptical; 

 external surface smooth, so far as known. Sutures direct, without lobes or undula- 

 tions. Air-chambers very deep. The specimen upon which the species is 

 founded is imperfect at the apical end, but retains most of the body-chamber. It - 

 length is L'D mm.: its lower diameter 2 mm.; its apertural diameter, 3.5 mm. It 

 bears fourteen air-chambers in a length of 21 mm., the body-chamber being 8 mm. 

 in length. 



Formation and locality. -In the. Galena shale* at WjrkofT, Minnesota. Collection of Dr. ( II 

 Bobbin*. 



ORTHOCERAS MrLTicAMKRATm Emmons, 1842. 



Ortkoctrai multieamerattu EMMOMS, 1842. Geology I -rk. Itopt . S. < -..r..l : '!, flg. W. 



OrthceeraM m*lticamrratxm HALL, 1847. Pala-ontolojjy of New York, vol. I, p. '.. ;.. \i. '..- 



Original description: "Extremely elongate, slender, very gralually tapering to 

 an acute point: surface apparently smooth or girt with -light undulations; septa 



