172 



THE CRINOIDEA 



FIG. LXXXIV. 

 Analysis of cup of Carabocriniis. 



SUB-ORDER 1. Cyathocrinoidea. Dicyclica Inadunata, with a fairly 

 stout tegmen, in which 5 orals (A, sub-ambulacrals, interradials, con- 

 solidating apparatus, of authors) are usually conspicuous, helping to 

 stiifen the tegmen, supporting the ambulacra on their adjacent edges, and 

 enclosing but not covering the peristome ; post. frequently a madre- 

 porite ; radial facet usually narrow ; arms distinct from dorsal cup, un- 

 branched or dichotomous ; none attain the pinnulate stage, but the 

 presence of pinnules would not in itself remove a genus from the sub-order. 

 FAMILY 1. CARABOCRINIDAE. Cyathocrinoidea with one or more 

 large anals in line with RR ; RA supporting these, and resting on a 

 supplemental plate intercalated between post. B and r. post. B and rest- 

 ing on IBB. Anus, surrounded by a few small plates, pierces tegmen 

 between x and post. O. Strong stereom- folds pass across the radio- 



ora ^ su ^ ures - Post. O pierced by hydro- 



R I-*! Ill pore (a madreporite). Arms stout and short. 



Genera Carabocrinus, Billings (1856,-59) ; 

 Strophocrinus, Sardeson (1899), both Ordo- 

 vician, N. America (Fig. LXXXIV.). The 

 radio -oral folds are probably vestigial 

 hydrospires (cf. Hylocrinus). The inter- 

 radial tegminal plates are admittedly homologous with orals, and ambu- 

 lacrals rest on their apposed edges (as in Fig. V. 2 ; see also p. 126). 

 FAMILY 2. PALAEOCRINIDAE. Cyathocrinoidea with anal x in line with 

 RR ; RA smaller and rhomboidal, abutting on x and not separating 

 r. post. Rs from r. post. B ; anal tube slightly developed ; 5 surround a 

 pentagonal peristome ; post. a madreporite ; arms narrow, rising from 

 well-defined facet, axial canal not separate from ventral groove, but passes 

 into thecal cavity through a large opening between R and adjacent 

 0. Genera Palaeocrinus, Billings (1859), Ordovician, Canada (Fig. 

 LXXXV). ; usually regarded as a synonym of Dendrocrinus, to which it 

 is closely allied ; but it differs in shape of RA, the denned radial facet, 

 the anal tube composed 

 of but 4 or 5 vertical 

 rows of plates, and above 

 all, the solid orals sup- 

 porting ambulacrals, 

 differentiae which place 

 it in this sub -order. 

 Stem shows 5 radial 

 sutures ; cup - plates 

 usually folded ; arms 

 isotomous to IVBr. 

 Porocrinus, Billings (1856-59 ; see J. Grant, 1881, and Beyrich), 

 Ordovician, Canada and Russia (Fig. LXXXVI.) ; arms unbranched. 

 Deep folds lie at the angles of all thecal plates, directed towards the 

 angle, and not passing at right angles across the middle of the sutures, 

 thus differing from hydrospires of Eublastoidea and from pectinirhombs ; 

 Beyrich imagined them to be separated by suture from the rest of the 

 plate, and Grant described a membrane [?a film of epistereom] covering 



IB 



Fio. LXXXV. 



Analysis of cup of Palaeocrinus, showing the axial 

 folds of the plates. E' radianal. 



