222 CATALOGUE OF THE BLASTOIDEA. 



base resembles that of Granatocrinus in being small and flattened, or slightly 

 concave (PL VI. fig. 17), though it is deeply so in one American species, which may 

 belong to this genus, and protuberant in others. In all the four species which we 

 definitely refer to it, the summit is exceedingly small and contracted (PL III. fig. 1 ; 

 PL VI. fig. 16 ; PL VIII. fig. 9 ; PL XVI. fig. 12). 



The relative proportions of the radial and deltoid plates of Schizoblastus are 

 extremely variable, just as in Granatocrinus. The radials of S. melonoides and S. 

 Bailii are very long, and form the greater part of the calyx (PL VI. fig. 15 ; PL XVI. 

 fig. 13), just as in Granatocrinus Norwoodi (PL II. figs. 32-35 ; PL VII. fig. 6), 

 while the deltoids are proportionately small. On the other hand in Schizoblastus 

 Sayi and in S. Bofei (PL VIII. fig. 10) almost the whole of the calyx is formed by 

 the deltoids, and the radials only enclose the distal ends of the ambulacra just as in 

 Elceacrinus and in Granatocrinus Derbiensis (PL II. fig. 46 ; PL IX. figs. 1-4, 6). 



The spiracles of Schizoblastus are minute slit-like openings which are chiefly 

 formed by lateral notches in the proximal ends of the deltoids. In the type species 

 (S. Sayi) they are some little way from the peristome, and the lancet-plate, with the 

 side plates resting upon it, comes up well between the spiracles (PL III. fig. 3) ; but 

 in S. melonoides, S. Bofei, and S. Bailii the spiracles are closer to the peristome, and 

 not so markedly separated by the lancet-plate, as the ambulacrum becomes distinctly 

 narrower between the spiracles (PL VI. fig. 16 ; PL VIII. fig. 9 ; PL XVI. fig. 12) ; 

 while the portion of the deltoid which intervenes between the two spiracles of each 

 interradius is much smaller than in S. Sayi (PL III. figs. 1-3). In the two Irish 

 species (PL VIII. fig. 9 ; PL XVI. fig. 12) there is a compound anal spiracle in the 

 posterior interradius just as in Cryptoblastus (PL VII. fig. 14) ; and we have some- 

 times thought that the same was perhaps the case in S. melonoides ; but the condition 

 of our specimens does not enable us to satisfactorily decide this point. In S. Sayi, 

 however, the central end of the posterior deltoid is considerably enlarged and raised 

 into a sort of projecting hood, which not only covers the anal opening, but also 

 extends outwards over the spiracles at its sides. These are only separated from the 

 anus by two thin partitions, such as Roemer J found in the anal spiracle of Pen- 

 tremitcs Godoni ; and if the hood of the posterior deltoid in S. Sayi were only a 

 little more arched, it would convert the triple opening into an anal spiracle like that 

 of Pentremites. 



We do not know much about the hydrospires of Schizoblastus. In the Irish 

 S. Bofei there is only one sac on each side of the ambulacrum (PL XVII. fig. 2), 

 just as in the British species of Granatocrinus (figs. 3-7); but in S. Sayi they are 

 much more complex, with four folds on each side, which lie very obliquely beneath 

 the ambulacrum and open above into an unusually large hydrospire-canal (fig. 1). 

 The lancet-plate of this type is pierced by three canals like that of Metablastus 

 1 Arehi\ f. Naturgesoh. 1851, Jahrg. xvii. ]kl. 1, t. 1. f. 2, :'>. 



