376 PALEONTOLOGY OF ILLDs T OIS- 



ranged above. A small interaxillary piece is also interca- 

 lated between tlie secondary radials of each ray. 



Vault prominent, and usually sloping up to the base of 

 the ventral tube ; composed of moderate sized convex or 

 tumid pieces ; ventral tube or proboscis very long, and 

 gradually tapering to the smaller extremity, where the 

 round opening is seen to be not more than 0.05 of an inch 

 in diameter. 







Arms twenty, short, or less than half as long as the ven- 

 tral tube, rounded on the dorsal side, and rather rapidly 

 tapering, Pinnulse slender, closely crowded, and composed 

 of joints two to three times as long as wide. 



Surface of body plates nearly even, or sometimes a little 

 convex, and nearly smooth ; sutures not impressed. Col- 

 umn stout, long, round and scarcely tapering ; composed 

 near the body of rather thick joints with rounded edges, 

 alternating with thin discs, which do not always show at 

 the surface, being as it were, impressed into the upper and 

 lower surfaces of the thickest pieces ; farther down the 

 pieces are all thick, and of uniform size, being scarcely 

 twice as wide as thick ; internal cavity small, and nearly 

 round, or obscurely pentagonal. 



Length of body, 1.65 inches ; breadth of do., at the arm- 

 bases, 1.25 inches ; length of proboscis, 3 inches ; thick- 

 ness of same at smaller end, 0.10 inch ; length of arms 

 about 2 inches. 



Some varieties of this species, and B. Christy i, Slmmard (sp.), resemble 

 each other closely, but the body of the latter species is nearly always 

 more depressed and broader, so as sometimes to approach a wheel- 

 shape. A more important diiference, however, is to be observed in the 

 number of arms, which in the Christyi is forty instead of twenty, there 

 being always two arms springing directly from each arm opening, in 

 that species. The arms of B. Christyi are also more slender. Onr 

 B.pistillus, and B. pistilliformis, are also allied to the form under con- 

 sideration, but differ in various details. 



Dr. SHUMARD gave good figures and an accurate description of the 

 body of this species, in the Missouri report ; but we have refigured and 



