THE CRINOIDEA 169 



England ; globose cup of heavy short plates, with tegmen from flat to 

 conical ; 0, radial dome-plates, and Amb usually distinguishable (Fig. 

 XLII.) ; free rami grouped in pairs, have covering-plates and side-plates. 

 Gennaeocrinus, W. & Sp. (1881-97), Devonian, N. America ; low cup of 

 thin plates with axial folds ; theca rather depressed and lobed in arm 

 regions ; O small but visible, as also are Amb ; rami, 8 to a ray, branch 

 from alternate sides of arms ; in form like the Actinocrinid Physetocrinus. 



SUB-ORDER 3. Actinocrinoidea. RR in lateral contact except in 

 post. IR ; proximal anal hexagonal ; IBrj usually hexagonal ; BB 3 

 equal, forming a hexagon. 



FAMILY 1. ACTINOCRINIDAE. Cup conical or bowl-shaped, with orna- 

 ment of axial folds ; only 1 IIBr, which is axillary ; free arm-rami branch 

 on alternate sides of the half-rays, starting either from lax or I lax ; all 

 free portions of arms are biserial ; proximal pinnulars bear hooks ; iBr 

 numerous, primitively merge into iAmb, but become separated therefrom 



Fio. LXXX111. 



Actinocrinus. 1, analysis of part of cup, showing post, and r. post, interradii. 2, cup from 

 below ; the supplementary plates shaded. 



by development and lateral contact of fixed brachials ; post. IR wide, 

 with proximal anal followed by 2 plates in second row ; tegmen 

 solid ; O not prominent, but usually distinguishable ; iAmb may cover 

 the tegminal Amb ; anus either on a tube or piercing tegmen, either 

 central or eccentric ; stem round, with small 5 -lobed lumen. The 

 family is confined to the Lower Carboniferous, and flourished chiefly 

 in N. America. Actinocrinns, with its descendant Steyanocrinus, and 

 Cactocrinus, with its descendant Teleiocrinus, form a group characterised by 

 a long anal tube. In Physetocrinus and its descendant Strotocrinus the anus 

 pierces the tegmen directly. For complete account of the family and 

 revision of genera see W. & Sp., 1897. Genera Actinocrinus, Miller (1821; 

 synn. Amphora, Cumb. ; Blairocrinus, S. A. Miller; Fig. LXXXIIL) ; cup- 

 plates with axial folds and parallel ridges ; theca lobed at arm-regions, the 

 numerous iBr being depressed, while the higher orders of Br with their 

 Amb form 5 broad rays, sometimes including some iBr ; these rays fork and 

 give off free rami to alternate sides every second or third plate, first on outer 

 side from Ilax, then on inner side from 1 1 lax, and so on ; the ramimay branch 

 again ; pinnules long, the proximal pinnulars armed with a small hook pro- 

 jecting from the middle ; tegmen solid, rising centrally into a stout tube with 



