50 



The vault ia very evenly convex aud bears a subcentral azygous 

 orifice. No proboscis. It is covered with plaue, smooth, polygonal 



plates. No ovarian pores discovered. 



This species bears no resemblance in form to either of the 

 twenty-four-armed species heretofore described. It would be classed 

 with the i-otund forms having smooth plates and no proboscis and 

 ranging from B. doderaddctylus with twelve arms to the present 

 species. 



Found in the Ijiirlington Group, at Burlington, Iowa, and now 

 iu the collection of A. Albers. 



BATOCEINUS SUBOVATUS, D. Sp. 



Plate II, Fig. 30, azygous side; Fig. 31, opposiie view. 



Species medium size, and general form rotund or subovate; cal^x 

 and vault subequal in size. No radial ridges. Plates plane and 

 smooth. Arm openings directed above an horizontal line and not 

 visible in a basal view. 



Basals form an hexagonal disc a little larger than the diameter 

 of the column, which bears a concave depression for the attach- 

 ment of the column. First primary radials about one half wider 

 than high, three hexagonal, two heptagonal. Second primary 

 radials quadrangular, two or three times as wide as long. Third 

 primary radials a little larger than the second, pentagonal, axillary, 

 aud the ray on the right of the azygous area bears upon each superior 

 sloping side two secondary ladials, the last being axillary, and one of 

 which bears upon each upper face two tertiary radials, and the 

 other bears upon the distal side, two tertiary I'adials, and upon 

 the proximal side, one axillary, tertiary radial, which supports 

 upon each upper side a quaternary radial, which gives to this ray 

 five arms. In the ray on the left of tlie azygous area, the third 

 primary radial bears upon each upper side, two secondary radials, 

 the last being axillary aud supporting, upon each upper side, two 

 tertiary radials, which gives to this ray four arms. Iu one of the 

 lateral rays, the third primary radial bears upon one side four 

 secondary radials, and upon the other, three secondary radials, 

 the last being axillary aud supporting on each upper side two 

 tertiary radials, which gives to this ray three arms. In the other 

 lateral ray, the third primary radial supports, on one side, three 

 secondary ladials, aud upon the other, one which is axillary aud 

 supports, on one side, three tertiary radials, and on the other, two 

 tertiary radials, which gives to the ray three arms. In the ray 

 opposite the azygous area the third primary radial supports, on 



