96 CATALOGUE OF THE BLASTOIDEA. 



and find a new generic name for the remaining species hitherto referred to the 

 genus, as hinted on p. 37. 



The hydrospires of Astrocrinus seem also to have been more or less completely 

 enclosed within the substance of the radials (PL XX. figs. 3, 4, 17-20) ; and the 

 same was perhaps the case with Stephanocrinus. So far as we can judge from the 

 scanty material at our disposal, the condition of the hydrospires beneath the regular 

 ambulacra of Eleutherocrinus is very much as in Mesoblastus and Granatocrinus 

 (PI. XIX. figs. 3, 4). The two hydrospire-plates form a bed for the lancet-plate ; 

 and the side plates rest partly upon the latter and partly upon the sloping edges of 

 the thin radials. The row of pores between the hydrospire-plate and the radials 

 leads down into a constricted hydrospire-canal from which the individual hydrospire- 

 tubes are given off laterally, so that they lie six-deep beneath each of the radial limbs 

 (PL XIX. fig. 3). The nearest approach to this condition in other Blastoids occurs 

 in Schizoblastus Sayi (PI. XVII. fig. 1) ; but the tubes seem to disappear altogether 

 towards the lower end of the calyx of Eleutherocrinus, a thickness of 4 millims. 

 separating the sections represented on PL XIX. figs. 2, 3. This appears to be due, 

 however, rather to the unusual shortness of the hydrospire-sacs than to their being 

 enclosed within the substance of the radials, no trace of them appearing in the 

 section figured in PL XIX. fig. 2. 



2. The Spiracles. 



The name " spiracles," as already explained, was suggested by Billings l for the 

 ring of five or ten openings immediately surrounding the peristome of a Blastoid, and 

 by which the more or less concealed hydrospire-apparatus communicates with the 

 exterior in all ordinary Blastoids except some species of the Codasteridae, in which 

 types the slits open directly to the exterior (PL XL figs. 1-6 ; PL XII. figs. 1-6 ; 

 PL XIII. figs. 1, 4, 6, 8-12, 14). Their relations to the deltoids, lancet-plates, and 

 side plates vary considerably in the different genera, and seem to us to afford valuable 

 characters for systematic purposes. 



In the only species of Cryptoschisma (PL V. figs. 23, 24 ; PL XIII. fig. 20), and 

 in those species of Phamoschisma which have broad ambulacra, the spiracles, when 

 present, are mere gaps which remain at the proximal ends of the radial sinus, owing 

 to the side plates being so small that they do not come into contact with the deltoids. 

 A small opening is thus left, which leads downwards into the sinus beneath the 

 covering formed by the more distal and broader side plates. We have seen these 

 openings, although they are very minute, in some specimens of Phmioschisma caryo- 

 phyllatum, as is represented in lloemer's figure 2 , and they would also appear to 



1 Amer. Journ. Sci. 18(59, vol. xlviii. p. 82 ; Ann. & Mag. Nat, Hist. 1870, vol. v. p. 264. 

 - Archiv f. Naturgesch. 1851, Jahrg. xvii. Bd. i. Taf. iv. fig. 1G C . 



