94 CATALOGUE OF THE BLASTOIDEA. 



Mesoblastus and Troostocrinus Reinwardti (PI. XVII. figs. 9, 10, 17 ; PI. XVIII. fig. 4). 

 P. Godoni and P. conoideus have four, like Schizoblastus Sayi and Troostocrinus {%) 

 Hneatus (PI. XVI. fig. 19 ; PI. XVII. figs. 1, IS ; PL XVIII. fig. 6). The P. sulcatus 

 of which we have made sections has four folds on one side and five or even six on 

 the other (PI. XVI. fig. 20; PL XVIII. fig. 5). The latter condition is due to a 

 branch being given off from one of the lamellar tubes for a short distance, but not 

 extending to any great length, as there is no sign of it in the section of the same 

 calyx which is figured on PL XVI. fig. 20. Lastly, Pentremites pyriformis, like 

 Orophocrinus verus, has seven hydrospire folds (PL XVII. fig. 13; PL XVIII. 

 fig. 3). 



In the broad ambulacra of Pentremites the side plates rest against the edges of the 

 lancet-plate ; and when the whole tripartite structure is removed the hydrospire-slits 

 are directly exposed (PL I. figs. 6, 7 ; PL XII, figs. 13, 14). For the inner wall of 

 each hydrospire-sac (/. e. that nearest the middle line) is not continued upwards above 

 the slits, so that it appears on the surface of the ambulacrum as the hydrospire-plate 

 as in Mesoblastus and Granatocrinus (PL IV. fig. 4 ; PI. VI. fig. 10; PL VII. fig. 15 ; 

 PL VIII. fig. 6 ; PL X. figs. 11, 12 ; PL XL figs. 14, 15). 



In a species with many hydrospire-folds, however, such as Pentremites pyriformis, 

 only a few of the slits are exposed by the removal of the lancet-plate and side plates, 

 for the remainder are hidden beneath the under lancet-plate (PL I. figs. 6, 7 ; PL XII. 

 fig. 13); while in P. Godoni (PL XII. fig. 1G) they are all as completely concealed 

 by it as those of Granatocrinus or Mesoblastus by the hydrospire-plate (PI. IV. fig. 4 ; 

 PL X. fig. 11). Owing to the complete continuity of the under lancet-plate across 

 the middle line of the ambulacrum we do not think that it can be compared to the 

 hydrospire-plate of Granatocrinus as implied by Hambach L For the latter dips 

 down into the interior of the calyx without meeting its fellow, as shown in PL X. 

 figs. 12-14, and our sections show that the same is the case with the corresponding 

 part of the hydrospire-sac in Pentremites (PL XVI. figs. 19, 20 ; PL XVIII. 

 figs. 3-5). 



Just in the same way as the proximal end of the hydrospire-sac of the Pent.remi- 

 tidae is more or less completely supported on the deltoid plates (PL I. figs. 6, 7 ; 

 PL XII. fig. 13), so the distal end is received into the substance of the radial very 

 much as already described in Cryptoschisma and Orophocrinus. In these types, how- 

 ever, the line of the hydrospire-folds is nearly at right angles to the body of the radial 

 (PI. XVI. figs. 3, 4, G) ; while in Pentremites the axis of the radial coincides with 

 that of the hydrospire-folds (PL III. figs. 6, 8, 9). The way in which this occurs is 

 well seen in Pentremites conoideus. Fig. 8 on PI. XVIII. represents the distal end 

 of a radial of this type after removal of all the ambulacral structures, together with 



1 Trans. St. Louis Acad. Sci. 1884, vol. iv. no. 3, p. .>jS. Bee antca, chap. iii. pp. 45-50. 



