SOME NEW BRACHIOPODS AND GASTROPODS 2lJ 



of the sinus and the mesial fold dividing as in the typical form of the 

 species. Sinus slightly to well developed but not usually well 

 defined. In the holotype the beak of the ventral valve is slightly 

 curved, but in many specimens, as the figured paratype, there is no 

 trace of a curve. 



This variety attains, on an average, a larger size than the typical 

 species. The width of the area as compared with the height is 

 about twice as great, and the sinus and the mesial fold attain greater 

 development than in the species as described by Hall and Whitfield. 

 The frequently inclined character of the area is also a point of con- 

 siderable diffeience for the area of 5. cyrtinaformis is regularly 

 almost vertical. This variety is much more inclined to develop 

 mucronate points than is the true species, especially in the young 

 forms. 



This species is apparently most unevenly distributed and of a 

 very gregarious chan cter, and the variety here described is no 

 exception to the habit of its species. At the pits of the Rockford 

 Brick and Tile Company I find the typical form much the more 

 common of the two; at Hackberry the variety helenae occurs 

 is proportionately larger numbers, particularly at the east portion 

 of the exposure. At hills north and west of Rockford I find it pre- 

 dominating and at the Bird Hill exposure, on the line between the 

 counties of Floyd and Cerro Gordo I find it almost replacing 

 the typical species. In this characteristic it makes an interesting 

 comparison with Spirifer Macbridei Calvin and Gypidula cowis 

 (Owen), both forms that are very gregarious in their habits. 



Holotype: — Number 865, collection of C. L. Fenton. Spirifer 

 zone, pits of the Rockford Brick and Tile Company, Rockford, Iowa. 



Paratype: — Number 866, collection of C. L. Fenton. Spirifer 

 zone, pits of the Rockford Brick and Tile Company, Rockford, 

 Iowa. Collected by author. 



Spirifer orestes Websteri nov. var. 



Shell small or medium, considerably wider than long, and usually 

 somewhat gibbous, and considerably extended on the hinge line, 

 both in young and old specimens. Valves marked by strong and 

 often coarse rounded or angular plications, simple on the sides of 

 the shell, but bifurcating d.nd occasionally uniting on the fold and 

 sinus, where there are usually four plications. Mesial fold strongly 



