CLASS III 



CRINOIDEA 



235 



sents the single columnal of Comatulids and the entire stem of the Pentacrinids. 

 The calyx is very large, and its plates, which are very thin, are strongly curved out- 

 wardly. Cretaceous. 



Subtrilje A. Marsupitids d'Orbiguy. 



Column wanting, probably represented by a large pentagonal plate called the 

 centrale,^ within the infrabasal circlet. Calyx large, p)("ifectly p)entameroiis, composed 

 of large thin plates, without interradials or anals ; greatest bulk belovj radials. Base 

 dicyclic plus the centrale, one of the largest plates in the calyx. Infrahasals five, 

 very large. Eadial facets narrow, crescentic, with a perforated transverse ridge. 

 Lower brachials much less than the width of ^ 



the radials, connected for a short distance 

 by interbrachials, but not strictly incorpor- 

 ated in the dorsal cup. Primibrachs two, 

 narrow. Arms small, apparently short, 

 with slender pinnules ; bifurcation on the 

 second primibrach, further branching un- 

 known. Tegmen unknown. 



The only known genus is Mar- 

 supites Miller {ex Mantell MS.), occur- 

 ring in the Upper Cretaceous (White 

 Chalk) of England, France and Northern 

 Germany, and in the Tombigbee Sand- 

 stone of Northern Mississippi. Its 

 general structure is on the Inadunate 

 plan, with remarkable development of 

 the basal portion, the infrabasals and 

 centrale constituting about half of the entire calyx (Fig. 338) 



Fig. 338. 



Marsujntes testudinarius (Schlotli). Upper Cre- 

 taceous ; Ijiineburg, Prussia, a, Calyx, natural size ; 

 h, Raciial, and a few of the arm-plates ; '•, Tips of arms. 



Subtribe B. Uintacrinids Zittel. 



Column wanting. Calyx large, perfectly pentamerous, greatest bulk above line 

 of radials, plates thin; interbrachial system greatly developed. Base dicyclic or 

 monocyclic; infrabasals present or absent in both young and adult of the same 

 species ; when present, five (but sometimes by resorption reduced irregidarly to three, 

 two, or one), very small, enclosing a small centrale, probably representing the stem ; 

 when absent, the centrale remains of about the same size, surrounded by the basals. 

 Interbrachials numerous, from the radials up, and often also in the second axil. 

 Primibrachs two, as large as the radials ; the secoml one axillary, followed by secundi- 

 brachs almost as large, passing gradually into free arms. Arms ten, unbranched, 

 very long and strong ; composed of very short, almost circular brachials, with frequent 

 syzygies, joint faces provided with transverse ridge, and pierced by an axial canal. 

 Pinnules stout and tapering, the lower ones incorporated into the calyx by lateral 

 union. Tegmen composed of a carbonaceous skin becoming black in the fossil state, 

 traversed by uncalcified ambulacra ; mouth margined ; anus subcentrcd, through a 

 strong, tufted tube. 



^ This plate is supposed by Carpenter to represent the distal plate of the stem, ami not the 

 proximal. A. H. Clark believes it, and the similarly situated plate in Uiniacrinus, to be the 

 homologues of the distal stem-plate, plus all the columnals of young Recent Comatulids. 



