61 



area are the shorter and of equal length, and, from these, there 

 is a gradual lengthening to the top of the third azygous plato. 

 All the plates are longitudinally convex and the sutures are 

 depressed, especially at the angles, and a pore penetrates the 

 calyx at every angle, and, on the longer sides, a pore pene- 

 trates the calyx between the angles. The greatest length of 

 the calyx does not equal the diameter. Plates thick. Column 

 unknown. 



Basals small, wider than long, and project below the end of 

 the column. Superior angles rather acute. Subradials the lar- 

 gest plates in the calyx and about as long as wide, thougli 

 somewhat unequal in size, three hexagonal, two heptagonal. 

 First radials about twice as wide as long, though of unequal 

 length, and slightly concave the entire width above for the re- 

 ception of the second radials, none of which are preserved in 

 our specimens. 



The first azygous plate is about as large as a first radial, 

 nearly equal sided, pentagonal, rests between the superior slop- 

 ing sides of two subradials, separates the first radial, on tlie 

 right, from the second azygous plate, on the left, and is trun- 

 cated above by the third azygous plate. The second azygous 

 plate is nearly as large as the first, truncates a subradial, sep- 

 arates the first radial, on the left, from the first and third 

 azygous plates, and tliins toward the ujDper edge, indicating 

 that it united with small plates belonging to a pi'oboscis. The 

 third azygous plate rests ujDon the first and in its lower part 

 separates part of the first radial plate, on the right, from the 

 second azygous plate and thins toward the upper edge, indi- 

 cating tliat it united with small plates belonging to the pro- 

 boscis. 



This is a peculiar species and on account pf its azygous area 

 and the pores that penetrate the vault, may yet be made the 

 typo of a new genus. At least it will not be confounded with 

 any species that has been lieretofore described in this genus. 



Found by K. A. Blair, in the Chouteau limestone, near So- 

 dalia, Missouri, and now in tlie collection of S. A. Miller. The 

 specific name is in honor of Prof. G. C. Bi'oadhead. 



