808 THE PALEONTOLOGY OF MINNESOTA. 



lUyrtoceras miuiicapolls. 



the ventral side. This implies that the depth of each chamber on the venter is 

 very much greater than on the dorsum. Each suture makes a low, broad and very 

 obscure saddle on the dorsum, scarcely perceptible lateral lobes, thence sloping 

 forward and making a strong ventral saddle. 



Sipho ventral and submarginal. Body-chamber large and deep on the dorsum, 

 equalling ten air-chambers in length, and on the venter six. Surface smooth. 



Dimensions. The specimen upon which this species is based retains the body- 

 chamber nearly intact, and thirteen air-chambers. It has a length of 36 mm. on 

 the outer curve, 11 of which belong to the body Chamber ; on the inner curve it 

 measures 28 mm., of which 11 belong to the body-chamber. Its transverse diameter 

 near the aperture is 14 mm.; at the last septum 13 mm., and at the thirteenth 

 septum 7 mm. Its dorso-ventral diameter near the aperture is 12 mm., at the last 

 septum 11 mm., and at the thirteenth septum 6 mm. 



This species is well characterized by the peculiar transverse form the shell. 



Formation and locality. The type specimen is from the Trenton limestone, and is believed to have 

 been obtained from Madison, Wisconsin. Collection of W. H. Scofleld. 



CYRTOCERAS MINNEAPOLIS, sp. nov, 



PLATE LIX, FIGS. 1-8. 



Shell arcuate, rapidly expanding to the aperture. Body-chamber without con- 

 striction ; apical curvature not known. Surface laterally compressed ; sides broad ; 

 dorsum narrow, venter still narrower and more arcuate. Transverse section 

 subelliptical, the major and minor diameters being as 11 to 9 at the next to the 

 last septum, and as 16 to 11 at the aperture. The lateral margins of the aperture 

 are convex, the dorsal and ventral margins broadly and narrowly concave or 

 re-entrant, respectively. The septa are regularly and evenly, though not deeply 

 concave, the deepest concavity being at about the center. The sutures are 

 transverse and simple, without lobes or saddles save for a slight upward inclination 

 on the venter, which gives to the air-chambers a greater depth on the ventral than 

 on the dorsal side. Sipho ventral, submarginal, expanded in each air-chamber. 



Surface covered with closely crowded concentric lines, conforming in curvature 

 to the aperture. On the internal cast are traces of longitudinal ridges over the 

 body-chamber. 



A small and typical example has the aperture 16 mm. in major, and 11 mm. in 

 minor diameter. At the next septum to the last these dimensions are 11 and 9 mm. 

 In a large specimen the aperture is 21.5x15 mm. and at the third septum from the 

 aperture 15x12 mm. This species has some similarity to Cyrtocems camurum 



