1881.] NATURAL SCIENCES OP PHILADELPHIA. 333 



The lateral branches either abut against each other or are partly 

 separated by small pieces, which, as we suggested, are rudiments 

 of earl}"^ pinnules. 



Interradials, anals, and interaxillary plates arranged as in the 

 preceding genus, but they are more numerous, and, contrary to 

 Teleiocrinus, extend far into the rim. 



Yault depressed, convex or more frequently flat, and only near 

 the arm bases somewhat rounded, the spaces along the ten main 

 divisions somewhat elevated above the general plane. The disk 

 is paved by many hundreds of small polygonal pieces, which de- 

 crease in size toward the arms, and which at the outer points of 

 the Ta,ys become almost microscopic. The apical plates are larger, 

 and are separated from each other, but not otherwise distinguished^ 

 from the other plates, and hence are not easily identified. 



Anus in form of a simple opening through the vault. The 

 inner floor of the vault is constructed similar to that of Physeto- 

 crinus, and has similar indentations (pores?) along the grooves; 

 but the divisions of the ray, within the rim, are separated as in 

 Teleiocrinus by partitions, and thus are formed into regular ducts, 

 which diverge until there is a separate passage to each ray. Arm 

 openings laterally arranged around the rim, each one with a 

 respiratory(?) pore aside of it. Arms long, comparatively thin, 

 not bifurcating in their free state ; pinnules long, composed of 

 slender joints. 



Column round, not large in proportion to the size of the speci- 

 men, without external rips or thickened processes ; central canal 

 of medium size, pentagonal. 



Geological Position, etc. — Strotocrinus seems to be limited to 

 the Subcarboniferous of the Mississippi valle}', and is here found 

 onlj^ in a small belt at the middle portion of the Upper Burlington 

 limestone, where it seems to have floiirished in great pi'ofusion, 

 but none reached up to the Keokuk Transition bed.^ The two or 

 three species of this genus belong to the largest and most beau- 

 tiful forms of the Palseocrinoidea, the body without arms attains 

 sometimes a height of five inches by six inches width along the 



^ The species which S. A. Miller describes from Bloomfleld, Mo., under 

 Strotocr. Bloomfieldensis is from cherty layers of the Upper Burlington, 

 and not from the Keokuk limestone ; we take it to be a synonym of Strotocr. 

 regalis until specimens showing the test prove the contrary, a diagnosis 

 based upon the internal cast only, has in our opinion very little value. 



