CLASS II 



BLASTOIDEA 



171 



chiefly formed by the apposition of notches in the lancet-plate and deltoids. 

 and Carboniferous. 



Devonian 



Nucleocrinus Conrad {Elaeacrinus Eoeiuer ; Olivanites Troost) (Fig. 266) 

 Basals small, inconspicuous, sometimes hidden within the columnar cavity 

 Eadials small, with very short limbs. Deltoids 

 greatly enlarged and elongated, forming over 

 two-thirds of the entire calyx ; the posterior one 

 wider than the others, and divided by a large 

 anal-plate. Lancet-plate exceedingly long and 

 narrow, partly exposed. Side-plates numerous ; 

 hydrospires two on each side of the ambulacra. 

 Summit covered by comparatively large orals, 

 asymmetrically arranged and forming a flattened 

 disk which completely closes the peristome. 

 Devonian (Onondaga and Hamilton Groups) ; 

 Indiana, Michigan, New York. 



Schizohlastus E. and C. {Crihroblastus Ham- 

 bach). Calyx resembling that of Orbitremites in 

 form. Basals almost always confined to the 

 lower face of the calyx ; deltoids of variable 



size, but always visible in a side-view. Hydro- Devonian ;Coiunibus, ex (after Roemer). 

 . f 1 , , c^ . , A, Side-view of calyx. />, Base. C, 



spires one to tour to each a,mbulacrum. Spiracles Ventral surface, i), same enlarged. 



small, slit-like, placed between the lancet-plates 



and deltoid ridges ; the posterior pair sometimes confluent with the anus. 

 Lower Carboniferous ; Ireland and North America (Kinderhook to Keokuk 

 Groups) ; Permian, Timor. 



Fio. 266. 

 Nucleocrinus rerneu Hi {Troost). Lower 



Family 6. Orbitremitidae Bather. 



Calyx globidar or ovoidal, with flattened or concave base, and long linear 

 ambulacra. Spiracles five, piercing the deltoids, or ten, grooving their lateral edges. 

 Lower Carboniferous. 



Orbitremites Austin (Granatocrinus Hall ex Troost MS. ; Cidaroblastus and 

 Globoblastus Hambach) (Figs. 253 A, 258 A). Calyx ovate to globose. Lower 

 face from slightly concave to deeply funnel-shaped ; interradial areas more or 

 less depressed. Basals small, generally concealed in the central columnar 

 cavity. Radials very variable in size, often long, and invariably turned in 

 below to assist in forming the base. Deltoids also variable ; usually unequally 

 rhombic, but sometimes triangular ; the anal deltoid frequently differing from 

 the others. Ambulacra nearly parallel-sided, always impressed within the 

 sinuses at their proximal ends. Lancet-plates narrow, not filling the sinuses, 

 and more or less exposed throughout two-thirds of the ambulacra. Side-plates 

 transversely elongated ; outer side-plates generally well developed. Hydro- 

 spires pendent, usually but two or three folds on each side of an ambulacrum ; 

 the inner one forming a well-defined hydrospire-plate. Spiracles five, piercing 

 the apices of the deltoids. Posterior spiracle larger, including the anus. 

 Summit closed by minute pieces which rarely exhibit any definite arrange- 

 ment. Lower Carboniferous ; England and North America (Burlington 

 Group), (?) Australia. 



