2l6 THE AMERICAN MIDLAND NATURALIST 



This variety is much less common than the typical form, particu 

 larly at the exposures in the Rockford district. I have found it more 

 pronounced at the Hackberry Grove exposure. 



Cotypes: — Set 897, collection of C. L. Fenton. Spirifer zone, 

 Hackberry Grove, Cerro Gordo County, Iowa. 



Atrypa reticularis alta nov. var. 



Young: — Shell depressed, suborbicular in extreme young, 

 sinus and mesial fold becoming developed earlier, however, than 

 in other types of the species Atrypa reticularis that I have examined. 



Adult: — Shell gibbous. Hinge line rather straight, and almost 

 equalling the width of the shell. The ventral valve becomes very 

 gibbous as the age of the shell advances. Sinus deep and abrupt; 

 mesial fold high but not well defined. The beak of the ventral 

 valve becomes recurved in aged specimens and finally incurving 

 over the beak of the dorsal valve. The plications are fine, as are 

 those of most of the Hackberry forms of Atrypa reticularis, though 

 those of alta seem finer than those of the average form. The shell 

 is marked by frequent lines of growth, usually of fine character. 



Holotype: — Number 156, collection of C. L,. Fenton. Spirifer 

 zone, Hackberry Grove, Cerro Gordo County, Iowa. 



Paratypes — Set 867, collection of C. L. Fenton. Spirifer zone of 

 Hackberry, Rockford, Iowa. Set 863, collection of C. L. Fenton, 

 St. Charles zone of Cedar Valley, Charles City Iowa. (Kelly 



Quarry)- 



This variety is quite distinct) and should not be confounded with 

 Atrypa rockford ensis Webster, which also has a deep sinus but is of 

 widely alate character. A. r. alta has much finer plications than 

 A. rockjordensis and does not develop the wide expansions that are 

 characteristic of the latter form. In the holotype of alta the mesial 

 fold is well pronounced and bounded by slight folds in the shell. 



Spirifer cyrtinaformis Helenae nov. var. 



Shell small, sub-trapezoidal, with slightly convex dorsal valve 

 marked by a practically undefined mesial fold. Cardinal area verti- 

 cal or strongly inclined forward and occasionally backward, three- 

 eighths to one half as high as wide in mature specimens, in young 

 often not more than one-third as high as wide, divided by a large 

 foramen and bearing vertical stria; . Surface of valves bearing from 

 thirty-five or more rounded plications, with the central plication 



