GENUS TROCHONEMA. 345 



the carina very slightly rounded ; while the lower side of the last volution 



is regularly rounded and somewhat ventricose. 



The surface has been finely striated with irregular undulations, corre- 

 sponding with the lines of growth where the striae have become crowded. 

 The entire length of shell to the base of the last volution is one inch and 

 nine- tenths, and the diameter near the base nine-tenths of an inch. 



This species is described from an impression in the limestone and a gutta 

 percha cast from the same. It is a well marked species ; differing from every 

 other in these rocks in the sharply carinate volutions and elevated spire. 

 In some characters it is allied to M. xantippe, Billings, but the spire is 

 more elevated : the length of that one, from the carina of the last volution 

 to the apex of the figure, is the same as the length from the same point to 

 the carina of the second volution above, in our specimen ; while the dia- 

 meters of the lower volutions in the two are about equal. 



Formation and locality. In limestone of the age of the Niagara group, 

 at Racine, Wisconsin. 



MURCHISONIA ? sp. 



In a paper by Mr. Billings, already cited, he has described Murchisonia 

 hercyna, a conical shell with flattened volutions and without a carina. 

 Among the Wisconsin collections from Racine there is a single specimen of 

 similar form, preserving about four or five volutions which are of precisely 

 similar character, except that they are a little more rapidly expanding, and 

 the two lower ones show a slight convexity of the upper part of the volu- 

 tion. The cast of the interior has the volutions subangular above and below. 



GENUS TROCHONEMA (Salter). 



TROCHONEMA FATUA (n. s.). 



Spire elevated ; shell turritiform, consisting of about four or five volutions, 

 which gradually increase to the last one which is moderately ventricose j 

 volutions biangular, leaving a flattened space upon the back about equal 

 to the flattened space between the upper angle and the suture line ; lower 

 side of the last volution rounded ; aperture ovate-elongate. 

 The specimens are casts of the interior, and in this condition are readily 

 distinguished from any other species of similar form in these rocks. 



A gutta percha cast shows the surface to be finely striated : the flattened 

 space on the back of the volution is margined on each side by a slender 

 carina, and the striae between are apparently coarser than those above or 

 below. The height of the specimens varies from less- than one inch, to one 

 inch and seven -eighths. The transverse diameter of the last volution is 

 about one inch, 



[January, 1865.] 44 ^^ 



