146 



THE CRINOIDEA 



an anal tube. Therefore for this line of descent, such a position of the 

 median dorsal rib of the anal tube is considered primitive (among Dicyclica 

 a similar stage is presented by Merocrinus). Anal tube somewhat com- 

 plicated. Stem markedly pentagonal, with 5 interradial sutures. Hetero- 

 crinus, Hall (1843, em. S. A. Miller, 1889, syn. Stenocrinus, W. & Sp.) ; 

 Ectenocrinus, Miller (1889) ; and Ohiocrinus, W. & Sp. (1886), are best 

 known from Ordovician, N. America, but certainly had representatives 

 in Europe, where also they were preceded in Cambrian seas by " Dendro- 

 crinus cambriensis" Hicks (1873), which seems allied to locrinus. They 

 agree in the transverse bisection of r. and 1. ant. RR, in addition to 

 r. post. R (exceptionally 1. ant. R is simple, and ant. R may be compound in 

 its stead) ; in the partial entry of the proximal plate of the anal tube into 

 the cup, since it now rests partly on 1. post. R, though more intimately 

 connected with r. post. Rs (Fig. XXVII.) ; in the departure from isotomy 

 in the direction of two rami with armlets. In Heterocrinus, Ohiocrinus, 



a 



Fio. LVIII. 



Heterocrinidae. 1, locrinus; 2, Heterocrimis bellevillensis ; 3, Ectenocrinus; 4, Anomalo- 

 crinus. 



and locrinus the stem is pentagonal and quinquepartite ; in Ectenocrinus 

 almost circular and tripartite. The anal tube is straight and narrow 

 in Heterocrinus and Ectenocrinus, spirally coiled in Ohiocrinus (cf. 

 Botryocrinus, Streptocrinus). Ectenocrinus has almost reached a pinnulate 

 stage of arm -branching, since the Br form syzygial pairs. Anomalo- 

 crinus, Meek & Worthen (1885 ; syn. Ataxocrinus, Lyon), Ordovician, N. 

 America, differs from the last three genera : (1) in greater irregularity of 

 RR, 1. post. R being larger than the others and often bisected vertically 

 (1. ant. R or ant. R, as well as r. post. R, are horizontally bisected as usual) ; (2) 

 in its peculiar arm-branching (Fig. LVIII. 4). Herpetocrinus, Salter (1873 ; 

 synn. Ophiocrinus, Charlesworth ; Myelodactylus, Ang. and [?] Hall ; [?] 

 Brachiocrinus, HalL Fully described, Bather, 1893), Silurian, Europe, 

 and probably N. America. Crown bent, in the transversal plane, back 

 on the stem, which is then coiled around it in the opposite direction 

 (Fig. LIX.). The coil could be tight, or could be uncoiled and the crown 

 exposed ; the movement was effected by an elastic ligament towards the 

 inner margin of the columnals, counteracted by strong muscles towards 

 the outer margin, the fulcrum being a transverse ridge. Columnals show 



