106 CATALOGUE OF THE BLASTOIDEA. 



its side, the border of which comes very near the ambulacrum. This indicates an 

 approach to the condition of the spiracles in Cryptoblastus mclo and Schizoblastus 

 Bailii (PL VII. figs. 14, 15 ; PI. XVI. fig. 12). 



On the other hand, the single spiracle is sometimes distinctly divided into two 

 parts by a septum, as in Granatocrinus McGoyi (PI. X. fig. S) ; and this condition 

 suggests a comparison with Pentremites elongatus, Mesoblastus Sowerbyi, or 11. elon- 

 gatus (PI. I. fig. 5 ; PL VI. fig. 13 ; PL VIII. figs. 2, 4). But the difference be- 

 tween the two types is really considerable ; for the spiracle of Granatocrinus is 

 entirely within the substance of the deltoid, while that of the Pentremitidae is 

 partly bounded by the side plates. 



Granatocrinus resembles Cryptoblastus and the two Irish species of Schizoblastus 

 (PL VII. figs. 14, 15; PL VIII. fig. 9; PL XVI. fig. 12) iu the fact that the two 

 posterior hydrospires have a common opening with the anus. The two hydrospire- 

 canals do not meet the rectum till just before they reach the surface of the plate, as 

 is shown in the internal casts (PL VII. figs. 3, 5, 7). 



This perforation of the deltoid pieces of Granatocrinus by the proximal ends of 

 the hydrospire-canals is a character which, so far as we know, occurs in no other 

 Blastoid, with the partial exception of the allied genus Heteroblastus. According to 

 Hambach 1 the " rostrum " of the deltoid piece in Granatocrinus Norwoodi " is 

 horizontally so expanded that Nature found it necessary to perforate the same, in 

 order to give an outlet to the ovulum ; " while in his second paper 2 he tells us that 

 the deltoid pieces of Granatocrinus are perforated " because the lancet-pieces do not 

 reach far enough to the summit to enter into the composition of the spiracle-openings." 

 He also gives a diagram of the summit in G. Nonvoodi, in which the proximal ends of 

 the lancet-pieces are represented as altogether outside the ring of spiracles, and rela- 

 tively as far from the peristome as they are in Orophocrinus stelliformis (PL XI. 

 fig. 9 ; PL XV. fig. 11). We quite admit that this is the case in some individuals, 

 as seen both on the exterior of the calyx and on the casts (PL VII. figs. 7, 10) ; but 

 even if it were universal, which it is not, we must confess that we cannot follow the 

 relation of cause and effect in Hambach's statement. For we do not see why the 

 relatively broad proximal ends of the deltoids should not be both perforated and 

 separated by the lancet-plates. Thus, for example, the lancet-plates of the Pentremites 

 elongatus represented on PL I. fig. 5, or those of P. hemisphericus (PL XVI. fig. 21) 

 come very close up to the mouth ; but we do not imagine that their position would be 

 altered in the least if there were a perforation in the middle of each deltoid instead 

 of the oral ridge. Neither do we understand how the perforation of the deltoids in 

 Granatocrinus Xonvoodi would be interfered with if they were a little further sepa- 

 rated, so that the lancet-plates could approach the peristome rather more closely than 



1 Trans. St. Louis Acad. Sci. 1880, vol iv. no. 1, p. 153. 

 - Ibid. 1884, vol. iv. no. 3, p. 545. 



