PLATYCEINIDiE. ggS 



slightly depressed. Eadials moderately spreading and somewhat irregular 

 in form; the two posterior ones fully as wide as long, the others a little 

 longer ; the median portions of the plates abruptly raised, forming a quad- 

 rangular elevation of which the margins are parallel to the edges of the 

 plates. Costals subtrigonal, rather short. Ventral disk convex, flattened at 

 the summit. The orals very large, the posterior one larger than the four 

 others ; the latter elongate, at the four regular sides of the calyx resting 

 against the first row of interradials, of which the middle one is wedo-ed in 

 deeply between the radials. The middle plate of the anal side is much 

 wider, and supports a number of small plates which form the anus. Ambu- 

 lacral plates few upon the disk. Anal opening excentric, directed upwards. 

 Structure of arms unknown. 



Horizon and Locality. — Lower Burlington limestone, Hannibal, Mo. 



Type in the collection of Wachsmuth and Springer. 



Remarls. — ToSs. species resembles P. sulspiimlosus Hall, but differs in the 

 form of the calyx and in the surface markings. 



The specific name is in honor of Eev. John Davis, of Louisiana, Mo., to 

 whom we are indebted for the type specimen. 



Platycrinus allophylus S. A. Millee. 

 Plate LXXI. Fig. 17. 



1S91. S. A. Millee ; Bull. 4, Geol. Surv. Missouri, p. 9, Plate 1, Tigs. 3 and 4. 



A small species, in its form unlike any other Platycrinus. Dorsal cup 

 slender, once and a half as high as wide, cylindrical to the top of the basals, 

 then expanding gracefully to the arm facets; the lower face broadly truncated. 

 Surface of plates apparently smooth ; their margins toward the basi-radial 

 and interradial sutures slightly beveled ; the interbasal sutures rarely visible. 

 Basals as long as the radials, forming a cylindrical cup with a short expanded 

 rim around the lower end, the bottom truncated, and slightly impressed for 

 the reception of the first stem joint, which occupies less than half the dia- 

 meter of the lower face. Eadials longer than wide, moderately expanding 

 above, rounded along the back, depressed at the sides, their facets projecting. 

 The latter occupy fully one half the width of tlie radials, and more than 

 a third their length ; they are semicircular, are deeply notched at the upper 

 end, and directed outward almost horizontally. Costals short and axillary ; 



