CLASS III CRINOIDEA 217 



forming a flexible network, which may be continuous all arouiul the crown 

 or be divided into five broad, reticulate, fan-like fronds. In the calyx of 

 some young specimens the radial facet is narrow, semicircular, evidently 

 beariiig the brachials in the usual succession. Axial canal distinct in arms 

 but not perforating radials, which are thin. Stern terminating in a thick, 

 branching root. Silurian ; Gotland, England and North America. 



Petalocrinus Weller, from the Silurian of North America and Gotland, 

 with its arms united by lateral fusion into five ponderous fans, has some 

 resemblance to Crotalocrinus, but seems to have no anal plate. It may be 

 nearer to the Gasterocrinidae. 



Family 9. Cyathocrinidae Roemer (emend. Wachsm. and Springer).^ 



DkycUc. Tegmen strong, composed of rather large orals more or less exposed^ 

 surrounding but not covering the peristome ; rigid amhulacrals supported on their 

 adjacent edges, meeting dbove the oral centre and often greatly modified ; and inter- 

 amhulacrals, which often encroach upon and ohscure the other plates. Posterior oral 

 frequently a madreporite. Anus located either in the posterior interamhidacrum 

 directly through the tegmen, or at the distal end of a plated anal tuhe, or dorsally 

 through the side of the cup. Arms non-pinnulate. Radial facet s usually semi- 

 circular, less than the width of the radial. Union of radials with proximal brachials 

 usually by incomplete articulation upon undifferentiated Joint faces, with concavo- 

 convex surfaces, without true transverse ridge, though with occasional traces of it. 

 Infrabasals usually five. Stem usually round. 



Subfamily A. Carabocrininae. 



Arms usually dichotomous ; heterotomous in some of the later genera. Radianal 

 obliquely to left of right posterior radial. Anal x present. Posterior oral usually 

 a madreporite. Infrabasals five. Stem usually round. Ordovician to Lower 

 Carboniferous. 



Carabocrinus Billings. RA completely separating BB, and having a 

 supplemental plate intercalated below it, touching IBB. Anal x large, in 

 line with radials. Anus directly through the teg- 

 men. Arms branching. Posterior oral pierced by 

 hydropore. Ordovician (Trenton) ; Canada and 

 Kentucky. 



Strophocrinus Sardeson. Ordovician ; Minnesota. 



Porocrinus Billings (Fig. 314). RA smaller, rhom- 

 boidal, not separating BB. Arms ten, unbranched. 

 Calyx plates deeply folded at the angles, but folds 

 do not cross the sutures or form true pore-rhombs. Fi«. 3i4. 



Anus in a slight protuberance. Referred by some ord^^r;" mTa^t" cÄ 

 authors to the Cystids. Ordovician: Canada, Ken- Nat. size (aoer Biiiings) ; h,p. 



, . T-- . "^ ' radiatus Beyr, Ordovician ; 8t. 



tUCky and KuSSia. Petersburg. Calyx plates show- 



Palaeocrinus Billings. RA as in preceding genus. i^;,*!/^^;!; ilVS'ßeyrSr 

 Arms branching several times ; slender, rising from 

 a small curved facet. Anal tube small. Ordovician ; Canada and Kentucky. 



Homocrinus Hall. RA as in preceding. Arms branching, strong ; radial 

 facets wider than usual in the family, nearly straight. Anal tube large, 



