A treatise on zoology . )latfs ; in post. IK is a vertical ridge of anals ; THE CRINOJDEA 165 stem relatively large and sub-pentagonal. Genus—Tanaocrinus, W. &Sp. (1897), Ordovician, Ohio (Fig. LXXVIII. 1, 2). In structure and intime this genus is well litled to Ije taken as an ancestor of the Carpo-crinidae. Family 2. Xknocrinidak. liatocrinoidea with 4 B15 ; eachhalf-ray contains IIBr, and sometimes lIIBr; free arms in zigzag orbi serial. iBr and ill Br, also illlBr when present, numerous. Post. IRwider than the others, divided by a longitudinal row of ridged of minute irregular
A treatise on zoology . )latfs ; in post. IK is a vertical ridge of anals ; THE CRINOJDEA 165 stem relatively large and sub-pentagonal. Genus—Tanaocrinus, W. &Sp. (1897), Ordovician, Ohio (Fig. LXXVIII. 1, 2). In structure and intime this genus is well litled to Ije taken as an ancestor of the Carpo-crinidae. Family 2. Xknocrinidak. liatocrinoidea with 4 B15 ; eachhalf-ray contains IIBr, and sometimes lIIBr; free arms in zigzag orbi serial. iBr and ill Br, also illlBr when present, numerous. Post. IRwider than the others, divided by a longitudinal row of ridged of minute irregular plates. Stem quadrangular to circular insection, with pentagonal lumen. Genera— S. A. Miller. Fig. LXXVIII. Tanaocrinidaeaml Xcnocrinidae. I, Tcuiocrinustypus,i>osteriov\\ew, x 2 diam. 2, anteriorview, X 2 diam. 3, Xenocrimis, analysis of cup. 4, Compsocrimis harrisi, cup from posterior,diagrammatic, x 2 diam. (All adapted from W. & Sp.) (1881 ; W. & Sp., 1897 ; Fig. LXXVIII. 3); iBr sink between RR, soas almost to rest on BB ; IIBr are finials. Compsocrinus, S. A. Miller(1883 ; W. & Sp., 1897 ; Fig. LXXVIII. 4), has RR in contact excepton anal side; IIIBr sometimes fixed ; IBr stouter than in Ordovician, Ohio, yl6acocnmis, Angelin (1878 ; syn. 1 Carolicrinus,Waag. & Jahn), Silurian, Gotland and (?) Bohemia, is more highly it and Gompsocrinus we must imagine a form in which the freeBr became biserial, while the free rami forked several times. In Ahaco-crinus the proximal biserial brachials (IIIBr) with their pinnules are in-corporated in the dorsal cup ; the stem has changed from sub-quadrangular 166 THE CRINOIDEA to circula
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