i So THE CRINOIDEA 



A similar evolution of arm-structure to that seen in Botryocrinidae 

 produced a long series of genera with pinnulate arms, for the most part 

 clearly forking into two rami, and rarely branching more than once 

 again, but in some genera branching more often. All at first had an 

 anal area more complicated than that of Dendrocrinus, in that a fresh 

 plate (rt) was inserted between x and r. post. R so as to rest on RA, 

 while a corresponding plate (It) appeared on the left of x. FAMILY 4. 

 SCAPHIOCRINIDAE ( = Poteriocrinidae, Auctt., greatly restricted). Dendro- 

 crinoidea with dichotomous, usually much branched, pinnulate, stout arms, 

 with facet occupying nearly full width of R ; with x, RA, rt, and It, in 

 anal area of cup, supporting a large plicated sac (Fig. XCIX.). Carbon- 

 iferous of N. America and Europe, a few Devonian. Genera Scaphio- 

 crinus, Hall (1858, em. W. & Sp., 1886 ; synn. Hydriocrinus, Trautschold ; 

 Abrotocrinus, Mill. & Gurl.), and Poteriocrinus, Miller (1821, em. W. & Sp., 

 1881), differ in little but the greater definiteness and less width of the 

 facet in the latter; each has a long anal sac (Fig. XXVI. 4). Woodocrinus, de 

 Koninck (1854 ; synn. Philocrinus, de Kon. ; Pachylocrinus, W. & Sp.), has 

 shorter cup, arms, and sac. In Aulocrinus, W. & Sp. (1897), the sac forks. 

 Zeacrinus, Hall (1858, em. W. & Sp., 1886), has a short, stout sac, around 



Poteriocrinus. FIG. XCIX. Zcacrinvs. 



Scaphiocriniclae. Analyses of cups. 



which the wide arms fit closely. Coeliocrinus, White (1863), and Hydreiono- 

 crinus, de Kon. (1858), differ from Zeacrinus in having the sac respectively 

 balloon-shaped and mushroom-shaped. Bursacrinus, Meek & Worthen 

 (1861 ; syn. Synyphocrinus, Trautschold), has arms like Zeacrinus, but no 

 anal except x in the cup ; it is in the latter respect the morphological 

 equivalent of Graphiocrinus (infra). FAMILY 5. SCYTALECRINIDAE. Den- 

 drocrinoidea with forked, pinnulate, slender arms ; anal structures as in 

 Scaphiocrinus. Genera Scytalecrinus, W. & Sp. (18 7 9,- syn. Dactylocrinus, 

 Sladen non Quenst.), and Decadocrinus, W. & Sp. (1879), both Carboniferous, 

 differ chiefly in shape of cup, conical in the former, saucer-shaped in the 

 latter, which thus leads on to : FAMILY 6. GRAPHIOCRINIDAE. Dendrocrin- 

 oidea with forked pinnulate arms and saucer-shaped cup, concave at base, 

 and containing x, but no RA (Fig. C.). In many points resemble the earlier 

 Encrinidae, but have not such thick cup-plates or large muscle-fossae. 

 Middle and Upper Carboniferous. Genera Graphiocrinus, de Koninck 

 (1853), Aesiocrinus, Miller & Gurley (1890), Delocrinus, Miller & Gurley 

 (1890 ; syn. Geriocrinus, White non Desor). In this and the succeeding 

 families the biserial arrangement of Br first assumes prominence ; it had 

 already appeared as an occasional gerontic character at the distal end of 

 the rami, but now is found in all except their most proximal portions, 

 accompanied by shortening of the arm. FAMILY 7. CROMYOCRINIDAE. 

 Dendrocrinoidea with simple or bifurcating, stout, pinnulate, usually 



