THE BLASTOIDEA 



folds distinctly portions of the thecal plates, coming to the surface of the 

 radial sinus. No distinct hydrospire-canal or pores ; spiracles developed 

 imperfectly or not at all. Genera Cadaster, PJuienoschisma, Cryptoschisma, 

 Orophocrinus. This family coincides with that of Etheridge & Carpenter. 

 FAMILY 2. PINTRKMITIDAE. Hydrospire-folds, usually numerous, concen- 

 trated at the lowest part of the radial sinus, and partly or wholly pendent. 

 Hydrospire-canal opens through spiracles bounded distally by side-plates. 

 Base convex. Ambulacra rather broad. Genera Pentremitidea, Pentre- 

 mites. This equals the Pentremitidae of Etheridge & Carpenter, minus 

 Mesoblastus. 



FIG. XV. 



Theeas of typical Blastoids. 1, a Codonoblasticl Pentremites robustus (from Brit. Mus. ES145). 

 2, a Troostoblastid Tricoelocrinus woodmani (from Brit. Mus. E8171). 3 and 4, a Granato- 

 blastid Orbitremites orbicularis (from the type-specimens, Brit. Mus. E8135). 3, from the side. 

 4, from below, with posterior interradius uppermost. All figures nat. size. 



Series B. TROOSTOBLASTIDA. FAMILY 1. TROOSTOCRINJDAE. Elongate 

 forms with linear ambulacra descending sharply outwards from the much 

 restricted peristome. Hydrospire-folds only slightly concentrated, but 

 communicate with exterior through pores, and through spiracles bounded 

 by A and lancet-plates. Genera Troostocrinus, Metablastus, Tricoelocrinus 

 This equals the Troostoblastidae of Etheridge & Carpenter. FAMILY 2. 

 ELEUTHEROCRINIDAE. Elongate, stemless, asymmetrical, with four narrow 

 ambulacra, accompanied by unconcentrated hydrospires. Fifth ambula- 

 crum shortened and widened. A minute. Genus Eknthcrocrinus. 



Series C. GRANATOBLASTIDA. FAMILY 1. NUCLEOCRINIDAE. Interam- 

 bulacra show traces of a primitive triad of plates. Ambulacra linear, and 

 stretching far down the theca, which is ovoid. Hydrospire-folds few and 

 pendent. Spiracles double. Mouth roofed by large plates firmly united 

 into a tegmen. Genera Nuclcocrinus, Schizoblattus, This family equals 

 Etheridge & Carpenter's Nucleoblastidae, minus Cryptoblastus and Acentro- 

 tremitcs. FAMILY 2. OUBITRKMITIDAE. Theca globular with concave or 

 flattened base. Ambulacra linear, stretching down to concavity of base. 

 Hydrospire-folds few and pendent ; a hydrospi re-plate always present 

 (unknown in Hetcroblastus). Hydrospire-folds rarely penetrate A, but long 

 canals pass onward, through, beside, or under them, except in Acentro- 

 tremites. Genera Orbit remitcs, Cryptoblastus, Heteroblastus, Mesoblastnx, 

 Acentrotremites. This corresponds to Etheridgc & Carpenter's Gfanato- 

 blastidae, plus Cryptoblastus, Mesoblastua, and Acentrotrcmites. FAMILY 3. 



