DESCRIPTIONS OF THE SPECIES. 200 



excavations of the base, together with the expansion of the lower pari of the calyx, 

 are sufficient to fix its generic position. It is an altogether smaller species than 

 Tricoslocrinus Woodmani, which has a much more deeply excavated base. 



Locality and Horizon. Spurgen Hill, Indiana: Warsaw Limestone, Subcarbo- 

 niferous. 



Family NUCLEOBLASTIB^l, E. & C, 1886. 



Definition. Calyx usually "lobular or ovoidal, with flattened or concave ba>e and 

 linear ambulacra. Spiracles distinctly double, and chiefly formed by the apposition 

 of notches in the lancet-plate and deltoids. 



lu marks. We have adopted the name Nucleoblasticke for this family in order that 

 the name Nucleocrinus, which was proposed by Conrad for its type genus, may not 

 be altogether lost sight of. It is explained elsewhere why we cannot agree with 

 Prof. J. Hall l , who conceives " that there can be no doubt as to the propriety of 

 restoring the earliest name" for the type which is now generally known as Elceacrinus, 

 Roemer ; and we have therefore done our best to prevent Conrad's notice of this 

 form from being altogether forgotten. 



The calyx is of a tolerably uniform shape among the different members of this 

 family, being usually globular or ovoidal (PI. II. figs. 43, 40 ; PI. VI. fig. 15 ; 

 PI. VIII. fig. 10 ; PI. XIII. fig. 18 ; PI. XVI. fig. 13 ; PI. XVIII. fig. 19), though it 

 lengthens out considerably in Elceacrinus obovatus, Barris. The base is relatively 

 small and either flattened or concave (PI. II. fig. 45 ; PI. VI. fig. 17 ; PI. XIII. 

 fig. 17); while, except in Acentrotremites (PI. XIII. figs. 18, 19), the ambulacra 

 are narrow and linear, as the side plates rest upon and not merely against the lancet- 

 plate (PL VIII. fig. 11 ; PL X. fig. 17 ; PL XVII. figs. 1, 19 ; PL XVIII. figs 16- 

 18). The spiracles are largely formed by notches in the flattened proximal ends of 

 the deltoid plates (PL III. figs. 1-3; PL VI. fig. 10; PL VII. figs. 14, 15; 

 PL XVI. fig. 12; PL XVIII. fig. 10) except in Acentrotremites, which lias its 

 spiracles on the lines of the radio-deltoid sutures (PL XIII. figs. 18, 19). In this 

 type, as also in Cryptoblastus and Elceacrinus (PL VII. fig. 15 ; PL XVIII. fig. 10), 

 the lancet-plate is likewise more or less incised, and so helps to increase the size of 

 the spiracle ; but this is not so clearly the case in Schizoblastus (PI. III. fig. 3). The 

 spiracles of this last genus are formed on somewhat the same plan as those of Meta- 

 blastus (PL HI. figs. 14, 15 ; PL VI. fig. 10) ; but on the other hand the Irish 

 species of it (PL VIII. fig. 9 ; PL XVI. fig. 12) have a summit not unlike that of 

 Mesoblastus, from which, however, they may be distinguished by the absence of an 

 hydrospire-plate. Mesoblastus thus forms a link between the Pentremitida? and the 



1 Fifteenth Ann. Kep. Xew York State Cab. Nat. Hist., Albany, 1S02, p. 145. 



2E 



