CAKBONIFEKOUS PElilOB. 155 



Genus ALLORISMA King, 1850. 



Allorisma subcuneata (var.) Meek and Hayden. 



Plate XII, fig. 7 a aud 6. 



Allorisma subcuneata Meek and Hayden, 1858, Proc. Acad. Nat. Sci. Phila., 263. 

 Allorisma subcuneata Meek and Haydeu, 1864, Paleont. of the Upper Missouri, 37. 



Shell of moderate size ; outline clavate-cuneate as seen by either dor- 

 sal or ventral view, oblong-suboval as seen by side-view ; posterior por- 

 tion laterally compressed ; antei-ior poiiion moderately gibbous ; beaks 

 depressed and placed about one-eighth of the length of the shell from the 

 anterior extremity ; posterior end abruptly rounded ; anterior end narrowly 

 rounded, somewhat prominent below and obliquely sloping above ; basal 

 margin straightened along the middle, but gently rounding before and 

 behind to meet the anterior and posterior borders respectively ; dorsal mar- 

 gin straight. Surface marked by distinct concentric undulations. 



Length, about six centimeters ; height, from base to cardinal border, 

 twenty-eight millimeters. 



Our specimens are in moderately good condition, but not entirely per- 

 fect, and, so far as they exhibit essential specific characters, they agi-ee with 

 those of A. subcuneata. They are, however, considerably smaller and rather 

 less gibbous anteriorly than the type-specimens of Meek and Hayden are, 

 and may possibly belong to a different species, yet I do not at present feel 

 warranted in separating them from that species except as a variety. Typ- 

 ical examples of the species are somewhat common in the Upper Coal- 

 Measure limestones of Missouri, Iowa, and Nebraska. 



Position and locality. — Strata of the Carboniferous period ; near Agua 

 Azul, New Mexico. 



