792 THE PALEONTOLOGY OF MINNESOTA. 



fTriptoceras planodorsatum. 



Formation and locality. In the Trenton limestone, Cannon Palls, Minnesota: in the Galena lime- 

 stone at Hader and Wykoff, Minnesota. Collection of W. H. ScoBeld. The original specimens were from 

 the Trenton at Beloit and Mineral Point, Wisconsin. 



Museum Register, No. 8288. 



TRIPTOCERAS PLANODORSATUM Whitfield, 1882. 



PLATE LVI, PIG. 4; PLATE LVII, FIGS. 2-4. 



Cyrloceras planodorsatum WHITFIELD, 1882. Geology of Wisconsin, vol. iv, p. 231, pi. vii, figs. 10-12. 



Shells small, compressed, slightly arcuate, the incurvature being on the dorsal 

 side. Lateral margins tapering slowly over the mature portions of the shell; ventral 

 side broadly flattened medially, lateral surface abruptly rounded; dorsal side 

 depressed convex. Transverse section broadly subtriangular, the base being the 

 ventral side. Minor and major diameters as 7 to 11. 



Septa gently convex, with a broad ventral lobe which is much more decided 

 than that of the dorsal side. Lateral saddles obtuse. Depth of the air-chambers 

 near the aperture about 15 mm., five being preserved in a length of 7 mm. Sipho 

 small, situated near the ventral side but not in contact with it. 



This species is represented by incomplete specimens, one of which, retaining 

 most of the body-chamber and six septa, has a length of 34 mm., a width at the 

 apertural end of 12 mm., and at the lower end of 10 mm. Another example repre- 

 senting only the body-chamber, is 31 mm. long, has an upper diameter of 14 mm., 

 and a lower diameter of 10 mm. 



Formation and locality. From the Trenton limestone at Minneapolis, Minnesota. The original 

 locality is three miles above Beloit, Wisconsin. 



TRIPTOCERAS OWENI, sp. nov. 



PLATE LVI, FIGS. 5-7. 



Shell small, unequally convex, slightly arcuate, with the incurvature on the 

 dorsal side; rapidly tapering; ventral side very depressed convex, nearly flat; dorsal 

 side decidedly convex, sloping with more or less abrupt curvature to the rounded 

 lateral margins. This dorsal convexity is rather more pronounced on the earlier 

 portion of the tube. Lateral margins approximating at an angle of about 20. The 

 external aspect of the shell is that of some large, slightly arcuate forms of Hyolithes. 



Septa slightly convex, the minor and major axis as 1 to 2. Dorso-ventrally the 

 convexity is very slight. The entire marginal section of the septum is rounded 

 subtriangular, the lateral saddles being narrowly obtuse. Sipho small, ventral and 

 submarginal. Surface of the shell apparently smooth. 



The single specimen of this very characteristic form has a length of 34 mm. 



