A treatise on zoology . inidaebecome extinct. Family 3. Acrocrinidae. Cupformed of 2 BB, forming a hexagon ; 5 RE, ; 1anal in line with RR ; and a large belt of acces-sory plates between BB and RR. Acrocri7ius,Yandell (1855, W. & Sp., 1897), later Carboni-ferous, N. America (Fig. LXXIII.) ; derived fromDicliocrinus, which it otherwise resembles, by thegradual intercalation of 6-20 circlets of supple-mentary plates, superbasals (SB) ; the SB im-mediately above BB are always the latest formed Acrocrimis amphora. (Re-and the smallest ; the SB supporting the anal and ZthTspringS!) ^t^ant. R are in
A treatise on zoology . inidaebecome extinct. Family 3. Acrocrinidae. Cupformed of 2 BB, forming a hexagon ; 5 RE, ; 1anal in line with RR ; and a large belt of acces-sory plates between BB and RR. Acrocri7ius,Yandell (1855, W. & Sp., 1897), later Carboni-ferous, N. America (Fig. LXXIII.) ; derived fromDicliocrinus, which it otherwise resembles, by thegradual intercalation of 6-20 circlets of supple-mentary plates, superbasals (SB) ; the SB im-mediately above BB are always the latest formed Acrocrimis amphora. (Re-and the smallest ; the SB supporting the anal and ZthTspringS!) ^t^ant. R are in single series, the rest alternate. In A. amphora the arms were recumbent on the cup and apparentlyimmovable. This remarkable family was the last to appear, and sur-vived all other Adunata and all Camerata. Order 3. Monocyclica Camerata ( = Camerata, W. & Sp. jxtrs). Monocyclica in which IBr, two in each ray(exc. Stereocrinus, HadrocrinuSyAlloprosallocrinus) and often succeeding orders of Br, are incorporated by. Fig. LXXIII. i6o THE CRINOIDEA iBr in the dorsal cup (becoming fixed brachials, Br), while the corre-sponding Amb are either incorporated in, or pressed below, the tegmenby iAmb ; all thecal plates united by suture, somewhat loose in theearliest forms, but speedily becoming close, and producing a rigid theca ;mouth and tegminal food-grooves closed ; arms pinnulate. The families may be grouped somewhat after the plan of Wachsmuthand Springer (1897), thus :— A. No anal plate in radial circlet of patina. BB usually form a pentagon. Melocrinoidea. B. An anal plate between RR in post. IR. BB form a hexagon. 1. Proximal anal heptagonal, succeeded by one or more in the same vertical series, between the ordinary iBr. Batocrin-oidea. 2. Proximal anal hexagonal, succeeded by no vertical series, but by 2 iBr. Actinocrinoidea. Whether Group B. was derived from some genus in Group A. is un-certain ; representatives of both groups are found in the Ordovician. Itis more probable th
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