CLASS II 



BLASTOIDEA 



171 



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

 and Carboniferous. 



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

 Basais small, inconspicuous, sometimes hidden within the columnar cavity. 

 Radiais 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. 



Schizoblastus E. and C. (CribroUastus Ham- 

 bach). Calyx resembling that of Orhitremites in 

 form. Basais almost always confined to the 

 lower face of the calyx ; deltoids of variable 



Size, but always Visible in a side-view. Hydro- Devonian ; Columbus, O.(afterRoemer). 

 . ' / ^ y ^ A, Side-view of calyx. B, Base. C, 



Spn*es one to four to each ambulacrum. bpiracles ventral surface. D, 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 verneuili (Troost). Lower 



Family 6. Orbitremitidae Bather. 



Calyx globular or owidal, with flattened or concave base, and long linear 

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

 Lower Carboniferous. 



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

 Globoblastus Hambach) (Figs. 263 J, 258 A). Calyx ovate to globose. Lower 

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

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

 cavity. Radiais 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 triangulär ; the anal deltoid f requently difFering from 

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

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



