CRINOIDEA 



191 



)elow the bifurcations. Base concave, forming an inverted cup. Dorsal cup 

 itrictly pentamerous ; no anal plate. Interbrachials large, not enclosing any 

 mal plates. Silurian ; England, Gotland and North America. 



Tribliocrinus Geinitz (Spyridiocrinus Oihlert). Lower Devonian ; Germany 

 tnd France. 



Technocrinus Hall. Like Melocrinus, but having ten strong, simple, biserial 

 'arms, which do not bifurcate in the free State. Interbrachials not enclosing 

 supplementary anals. Devonian (Oriskany) ; Maryland. 



Macrost i/locrinus Hall. Basais three, unequal. Anal interradius much 

 wider than the others ; its first row consisting usually of three plates, while 

 that in the four other interrays consists of a single inter- 

 brachial. Arms ten, simple and biserial. Silurian; North 

 America. 



Patelliocmius Ang. (Fig. 290). Basais three, unequal. 

 Arms biserial or of cuneate uniserial brachials. No anal 

 plates. Dorsal cup elongate. Silurian ; Gotland, North 

 America. 



Allocrinus W. and Sp. Basais three, unequal. Arms 

 uniserial. No anal plates. Dorsal cup depressed. Inter- 

 brachials few, Silurian ; North America. 



Briarocrinus Angelin. Silurian ; Gotland. 



Centriocrinus Bather (pro Cenirocrinus W. and Sp., non 

 Austin, nee Worthen). Basais fused. Dorsal cup depressed. 

 No anals. Arms unknown. Devonian ; North America. 



Dolatocrinus Lyon (Cacabocrinus Hall). Dorsal cup per- 

 fectly pentamerous, cup-shaped or saucer-shaped. Base u^ian ; Gotland. 

 usually concave. Basais primitively three, but completely ^^*^"r?\ ^^'"^^ ^^^^ 

 anchylosed in the adult. Costals two ; iBr few, the first 

 ones extremely large. Tegmen comparatively flat, and composed of rather 

 large plates, of which the orals form the summit. Respiratory pores be- 

 tween arm bases frequently present. Anus at the end of a short tube. 

 Arms little known, sometimes branching and biserial. Column with 

 numerous projecting rings and buttresses. Devonian ; North America. 



Stereocrinus Barris. Like the preceding, but the anchylosis of the BB 

 incomplete, and with only one costal. Devonian (Hamilton Group) ; North 

 America. 



Hadrocrinus Lyon {Coronocrinus Hall ex Troost). Dorsal cup extremely 

 large, with concave base ; basals closely anchylosed. Brachials to the fourth 

 or fif th Order incorporated in the cup. Interbrachials numerous and large ; 

 no distinct anal plate in lower ranges. Tegmen composed of innumerable 

 small plates. Devonian (Onondaga) ; Falls of the Ohio, near Louisville, 

 Kentucky. 



The type described under tliis genus has not hitherto been well understood. It falls into 

 two subdivisions, ditfering more strongly than Stereocrinus and Dolatocrinus ; one (/f. discus) 

 having few very heavy arms, and one costal ; the other {H. plenissimus) witli numerous very 

 slender arms, an^ two costals. 



Fig. 290. 



Patelliocrinus lepto- 

 -D„„p dactylus (Ang.). 8il- 



Family 6. Calyptocrinidae Angelin. 



Momcydic. Lower brachials and interbrachials forming an impmiant pari of 

 the dorsal cup, which above the base, is perfectly pentamerous. Plates of the calyx 



