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ci^Ass III CRINOIDEA 203 



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A. Anal plates, when present, partly or wholly incorpm'ated in the 

 calyx. 



Suborder 1. SAGENOCRINOIDEA. 



Family 1. Lecanocrinidae Springer. 



Infrabasals abutting on dorsal side of basals, more or less ered, and taking 

 pari in the calyx wall Crown usually small, short, rotund, with arms abutting, 

 frequently interlocking, and closely infolding at the distal ends. Silurian to Lower 

 Carboniferous. 



a. Rays in contact except at the posterior side, where anal x separates radials, toucliing 

 posterior basal. No iBr in other areas. 



Lecanocrinus Hall {Cyrtidocrinus Ang.) (Fig. 304). Arms dichotomous, 

 flat, interlocking. RA rhombic, obliquely below r.post.R. Anal x alone. 

 IBr two (exceptionally one). Silurian to Devon- 

 ian; North America, Gotland, England. 



Mespilocrinus Koninck and Lehon. No RA. 

 Anal X alone, or followed by a triangulär plate. 

 Arms dichotomous, usually rounded, with dex- 

 trose twist. IBr two. Lower Carboniferous 

 (Kinderhook to Upper Burlington) ; Belgium, 

 England and Mississippian area. North America. 



h. Rays above radials partly or wholly separated all FiGr7o4 



around, by *5r or perisome. Anal « usually between pos- ^ . , . '. .\ „., . 



terior radials, touohing basal (exception, SipUroainJ). o'tSTS^^TTn Ä thTS 



side, flgiire reversed (after Angelin). 



Homalocrinus Ang. Infrabasals very large, 

 enveloping basals, and sometimes radials. Arms heterotomous, with ten 

 main trunks, bearing ramules. Rays abutting above interbrachials, peri- 

 some not exposed interradially. Anal x, and large iBr in other areas, 

 followed by others. RA under r.post.R. between BB. IBr two. Silurian ; 

 Gotland, England. 



Calpiocrinus Ang. Like the preceding, but the rays have twenty main 

 trunks bearing ramules, and there is no RA. Silurian ; Gotland. 



These two genera are remarkably specialised in the enormous overgrowth 

 of the infrabasals, which envelop, and sometimes entirely conceal, both basals 

 and radials, a fact which has made them heretofore generally misunderstood. 



Cholocrinus Springer. IBB not enveloping BB. Arms heterotomous, 

 with ten main trunks bearing irregularly branching ramules. Rays not 

 abutting, divergent, not closely infolding; no regulär iBr, areas filled with 

 perisome. Anal x followed by perisome. RA rhombic, obliquely below 

 r.post.R. IBr two. Rays unequally developed, the two antero-lateral ones 

 being dwarfed. Type, Forbesiocrinus obesus Ang. Silurian ; Gotland. 



Anisocrinus Ang. Arms dichotomous. Rays abutting above iBr, perisome 

 not exposed. Anal x alone, or with others following ; iBr few, one large, 

 alone, or followed by others. RA more or less under r.post.R, above line 

 of BB. IBr two. Silurian ; Gotland, and North America (Western Niagara). 



Pycnosaccus Ang. (Oncocrinus Bather). Arms dichotomous. Rays not 

 abutting; no regulär iBr, areas wide, filled with perisome. Radial facets 

 much less than the width of R. Anal x alone, followed by perisome. JtA 



