788 THE PALEONTOLOGY OF MINNESOTA. 



lOrUioeeras olorus. 



Formation and locality. In the Trenton horizon at Minneapolis (Lake Street bridge), Pleasant 

 Grove, St. Paul, Cannon Falls and Fountain, Minuesota; in the Galena shales at Warsaw, Minnesota. 



The original specimens were from the lower and middle parts of the Trenton limestone at Middle- 

 ville and elsewhere, New York. 



Museum Register, Nos. 350, 381. 



ORTHOOERAS OLORUS Hall, 1877. 



PLATE LV, FIGS. 3 and 4. 



Orthoceras vertebrale HALL, 1847. Palaeontology of New York, vol. i, p. 201. pi. XLIII, flgs. 5a-c. 

 Orthoceras olorus HALL, 1877. In Miller's American Palaeozoic Fossils, p. 245. 



To this species are referred a few specimens with rather distant, narrow and 

 elevated annulations, which are slightly undulating and are traversed by alternating 

 elevated vertical strise and these crossed by extremely fine horizontal lines. None 

 of the material is good and such characters as are retained by the specimens show 

 no great dissimilarity from the original. The septum is moderately convex, the 

 sipho subcentral and the sutures, in the only example where clearly shown, follow 

 the annulations and lie in the bottom of the constrictions. The species has a general 

 resemblance to Orthoceras perroti, but differs in its more distinct and stronger 

 annulations. In one example there are nine annulations in a length of 45 mm.; in 

 another, five in a length of 25 mm. The diameter of the shell in both of these is 

 about 30 mm. 



Formation and locality. In the lower blue beds of the Trenton limestone, Mineral Point and Janes- 

 ville, Wisconsin; St. Charles and Holden, Minnesota; Galena shales, at Wykoff, Minnesota 



Museum Register, Nos. 252, 379, 8291, 8292. 



ORTHOCERAS TENUISTRIATUM Rail, 1847. 



PLATE LV. FIGS. 5 and 6. 



Endoceras proteiforme, var. tenuistriatum HALL, 1847. Palaeontology of New York, vol. i, p. 209, 

 pi. XLV, flgs. la-6; pi. XLVII, flgs. la-6, 2a-c. 



Shell long, straight, gradually expanding. Sutures direct; septum regularly 

 concave and very slightly oblique. Sipho subcentral, small. 



Surface of the shell without annulations or ridges; marked by fine, crowded 

 horizontal lines, somewhat undulating or irregular, often running into one another, 

 rounded on the summit and subimbricating, separated by low furrows and divided 

 at irregular intervals by a furrow of more than average width. These horizontal 

 lines and furrows are crossed by extremely fine vertical lines seen only under 

 magnification. Thanks to incarceration in the siphonal cavity of Cumeroceras, one 

 example of this species shows the surface ornamentation in a highly satisfactory 

 manner. It even retains a series of narrow vertical bands which do not in any way 



