CLASS III 



CRINOIDEA 



233 



of the axial canal, contrary to the general rule in dicyclic forms, directed 

 radially, corresponding with the outer angles of the stem. Stem of great 

 but unknown maximum length, having been traced for twenty feet without 

 reaching the end ; cirri very numerous, compressed or elliptical in section. 

 Lias and later Jura ; Europe. 



The Crinoids of this genus were 

 very gregarious, and flourished in 

 immense colonies. Exquisitely pre- 

 sci'ved specimens are found in the 

 Lower Lias of Lyme Regis, Eng- 

 land, and in the vicinity of Boll 

 and Metzingen, Wiirteraberg, which 

 have served as types of illustra- 

 tions in numerous works on Paleon- 

 tology. A slab containing no less 

 than twenty-seven perfect crowns 

 intertwined with stems and cirri, 

 may be seen in the U.S. National 

 Museum at Washington. 



Isocrinus Meyer (/sz's Linn. 

 pars; Encrinus Lamarck ^ars; 

 Cainocrimis Forbes ; Pideto- 

 crinus de Loriol ; Neocrinus 

 Wy V. Thomson ; Fentacrinus 

 sensu P. H. Carpenter). IBB 

 so far as known, present in 

 the adult, but visible only 

 when stem is removed. BB 

 forming a complete circlet, 

 or ^minute and separated by 

 lower angles of BE. Eadials 

 not projecting downward over 

 proximal columnals. Arms 

 about regularly dichotomous. 

 Columnals of circular, penta- 

 gonal or stellate section ; 

 sectors of joint-face distinctly 

 petaloid, with coarsely crenu- 

 late edges. Trias and Juras- 

 sic ; Europe and North 

 America. Recent ; West 

 Lidies (5-531 fathoms). 



Balanocriims Agassiz in 

 Desor. Columnals of circular 

 or hexagonal section, with crenellae around the edge only, not along the 

 sides of the sector. Trias to Eocene ; Europe. Known from fragments only. 



Austinocrinus de Loriol. Columnals have a joint surface as in Isocrinus, 

 but with finer striae radiating from the petals. Cretaceous ; Europe. 



Cenocrinus Wyv. Thomson. Recent; West Indies (5-531 fathoms). 



Endoxocrimis A. H. Clark (Diplocrinus Doderlein). Infrabasals resorbed 

 in the adult. Arms heterotomous, in two main rami with branches to the 

 inside of the dichotom ; the divisions are at the outer side of the rays only, 

 and consist each of two joints, united by syzygy. Recent ; West Indies. 



Fia. 337. 

 Fentacrinus {Extracrinus) fosslUs Blum. Lower Lias ; Lyme Regis, 

 England (after Goldfuss). a, Stem-joints of P. subangularis Mill. 

 Upper Lias ; b, Colnmn of P. hasaltiformis Mill. Middle Lias. 



