1879.] NATURAL SCIENCES OF PHILADELPHIA. 253 



PAL^EOCRINOIDEA. 



A SUBORDER OF THE CRINOIDEA. 



Body, as compared with recent Crinoids, larger; arms shorter; 

 test stronger. The latter is arranged on various plans, but is 

 alwa}-s composed of solid plates of which the interradials, in con- 

 trast to the Stomatocrinoidea, constitute important elements. 

 Plates of the aboral or dorsal side forming a cup, closed on the 

 ventral or oral side by a more or less solid integument, without 

 external food grooves or oral aperture. 



The food conve} r ed through openings at the base of the arms into 

 the body, and carried to the oral centre by means of internal or 

 subtegminal passages. Anus either in form of a plated tube or a 

 simple opening, subcentral or lateral. 



The introduction of water for respiratory purposes seems to 

 have been effected through small openings or pores which penetrate 

 the test. These openings, which in some groups were located in 

 the oral, in others in the aboral regions, seem to have been con- 

 nected with peculiar organs within the body, closely resembling 

 the so-called hydrospires of Cystideans and Blastoids. 



The Paleocrinoids, with but few exceptions, were pedunculate, 

 attached during lifetime. Flourishing abundantly in the Silurian 

 seas, they reach their climax in the Subcarboniferous, as well in 

 variety of form as in number of individuals, and they disappear 

 almost entirely during the Carboniferous, few forms, if any, sur- 

 viving as late as Mezozoic times. 



'o 



Family I. ICHTHYOCRINIDiE. 



(Diagram PI. 15, Fig. 1.) 



General form of the body including arms, globose to pyriform. 

 Column strong, perforation of medium size, generally pentangular. 



Underbasals three, of unequal size ; always small, often rudi- 

 mentary and not visible externally, being hidden by the column. 

 Basals five, moderately small, sometimes scarcely appearing be- 

 yond the column (in Calpiocrinus probably absent or imperfectly 

 developed). Primary radials, three to five by five, almost equal 

 in form and size. Radials of each order smaller by half than those 

 of the preceding, and of uniform size. Arms bifurcating, short, 



