40 



Geological Formation and Locality. In the shales above 

 the Galena limestone, on Makoqueta creek in Iowa, and 

 also on the east side of the Mississippi River, the particular 

 locality unknown. 



Collector. Br. Thomas Scott, of Dubuque, low. 



Dedicated to Prof. J. D. Whitney. 



CYRTOOERAS neleum, (n. s.) 



Description. Shell of small or medium size, very gradually 

 expanding from the apex and strongly curved, transverse sec- 

 tion circular, or sub-circular, very obtusely sub-angular on the 

 back in casts, most ventricose on the ventrolateral region. 

 Septa closely but not evenly arranged, averaging about nine 

 in a space equal to the transverse diameter of the shell, cur- 

 ving forward on the dersal side, their margins undulated es- 

 pecially towards the outer chamber where they become crowd- 

 ed. On the ventral side the septa have a broad advancing 

 curve. The exposed surface of the septa show the greatest 

 concavity a little on the ventral side of the centre. Siphun- 

 cle dorsal, comparatively large. 



Surface marked by transverse, slightly undulating annula- 

 tions, which are strongly and abruptly curved backwards on 

 the dorsum. Diameter of large specimens five-eights of an 

 inch. 



This species differs from C. lamellosum, Hall, 1847 — C. 

 Halleanus, D'Orbigny, 1850— C. Billingsi, Salter, 1859, (Can- 

 adian Organic Remains, Decade I.), not C. lamellosum of De 

 Verneuil, 1842, in the more gradual and equal curvature, the 

 much less rapid expansion, (the expansion being only one 

 sixteenth of an inch in a length of one inch and a quarter), 

 and in the position of the Siphuncle which is situated close 

 to the dorsal side. 



Geological Formation and Locality. In the "Buff limestone" 

 at Beloit, and forty feet above the base of the Trenton limestone 

 group, Platteville. 



Collectors. T. J. Hale and James Hall. 



CYRTOOERAS eugium, (n. s.) 



Description. Shell of medium size, strongly curved and 

 very gradually expanding from the apex. Section oblate, very 

 obtusely sub-angular on the back, rounded on the sides, and 

 depressed convex on the ventral side, giving the form of sec- 

 tion described, the transverse diameter of which is greater 

 jfchan the dorso-ventral diameter. Septa moderately convex, 



