ISO THE CRINOIDEA 



resembles an arm, and its presence was first notified in 1893. The relations 

 of the cup-plates, till then misunderstood, were thus shown to be essentially 

 the same as in the majority of Monocyclica, while the origin of Calycantho- 

 crinus, Mycocrinus, and Catillocrinus became clear. This was confirmed by 

 Jaekel (1895). Pisocrinus was shown by Wachsmuth to have 5 O sur- 

 rounding a peristomial space ; a groove passed along each interoral suture, 

 and probably conveyed the food-grooves to the central opening. The 

 rectum passed into the anal tube between post. and adjacent RR. An 

 anal tube is said by Jaekel to have been absent from the thinly plated 

 species of Triacrinus in Devonian slates. Calycanthocrinus, Follmann 

 (1887), Lower Devonian, Germany, shows a remarkable modification, 

 in the introduction of small arm -bearing plates (" pararadials " PR), 

 in the positions shown in Fig. LXII. 3. This may be compared with 

 the vertical bisection of a radial in Anomalocrinus or the addition 

 of 5 " interradial radials " in Promacliocrinus ; but it is the first stage 

 of a process continued in Catillocrinidae. It is heard to see how this 

 process could have been inaugurated except as a discontinuous meristic 

 variation (cf. Bateson, Materials for the Study of Variation, chap. xvii. 

 1894). FAMILY 6. CATILLOCRIXIDAE. Monocyclica Inadunata, in which 

 1. post. R and ant. R are much larger than the other RR, and bear PR, 

 usually fused to them ; no RA visible. Arms unbranched and non- 

 pinnulate. Anal tube resembling arms, but stouter, rests on left process 

 of r. post. R. Genera Mycocrinus, L. Schultze (1866, W. & Sp., 1886 ; 

 Jaekel, 1895), Middle Devonian, Germany (Fig. LXII. 4), differs from Caly- 

 canthocrinus in the suppression of RA and the PR borne by it ; the still 

 greater size of 1. post. R and ant. R, which now bear 6-7 arms apiece, i.e. 

 15-17 arms to the whole crown. The 3 BB become fused, while the 

 10-12 PR are usually fused with the large RR on which they rest. The 

 increase in size of the large RR takes place chiefly in the upper part ; all 

 the RR rest on the basal circlet, which forms a knob sharply separated 

 from them. Catillocrinus, Shumard ex Troost (1860, syn. Nematocrinus, 

 Meek & Worth en ; see W. & Sp., 1886), Lower Carboniferous, X. 

 America (Fig. LXII. 5). The cup has here resumed a shallow basin- 

 shape, and differs from Mycocrinus in the complete fusion of BB and the 

 still greater lateral extension of the 1. post. R and ant. R in their upper 

 regions. Those large RR now bear 15-31 arms apiece, there being 

 usually more on ant. R than on 1. post. R (cf. Calycanthocrinus). The PR 

 are absolutely fused with RR, or were never developed at all. The basal 

 circlet projects upward on 1. ant. side, but is almost hidden by the stem on 

 the other side. The arrangement and shapes of the plates curiously 

 resemble those which obtain in Halysiocrinus, while the arms may be com- 

 pared to the branches that spring from the main-axils in that genus. A 

 similar result has been attained by two lines of development, which, in 

 their initial stages, were as different from one another and from the 

 normal type as could well be. The relationship of these forms is a 

 problem that would repay yet deeper study. FAMILY 7. ZOPHOCRINIDAE. 

 Monocyclica Inadunata, with 3 BB, 2 equal and 1 larger ; 4 RR, 1 rather 

 larger than the rest, and probably equals r. and 1. post, fused ; 5 form 

 solid tegmen, post. being the largest, and r. and 1. ant. the smallest 



