THE HTDKOSPIKES \M> SPIBAOLES. 107 



they do in the specimen which Hambach figured. In fact, the lancet-plates of tin- 

 two posterior ambulacra do reach quite close enough to the summit to "enter into 

 the composition of" the anal spiracle, but they do not do so (1M. Nil. figs, ">, 7, I' 1 

 Another objection to the teleological argument which he employs is, that there are 

 some Blastoids, such as Orophocrinua stelliformis (PI. XI. fig. !) ; PI. XV. tig. 11). 

 in which the lancet-piece terminates sonic way from the summit, and the deltoid 

 not perforated; while there are many individuals, both of Grariatocrirma Nbrwoodi 

 and of other species of the genus, in which the lancet-plate comes quite close up to 

 the peristome. There is a considerable variation in G. Norwoodi in the degree of 

 approximation of the exposed parts of the deltoids, for in some individuals the la: 

 plate comes up between them, and actually separates two of the spiracles. This is 

 still better shown in our figures of G. McCoyi and of G. canvpanulatus (PI. X. figs. 8. 

 1U) ; for most of the side plates have fallen away, leaving their impressions upon the 

 lancet-plate, which comes quite close up to the peristome betwen the spiracles. 



This effectually disproves Hambach 's assertion that the deltoids of Granatocrinus 

 are perforated " because the lancet-pieces do uot reach far enough to the summit to 

 enter into the composition of the spiracle-openings," and shows the danger of gene- 

 ralizing upon insufficient data. 



The spiracular openings upon the surface of the deltoids of Granatocrinus are often 

 somewhat strongly marked, the proximal end of the plate having a different appear- 

 ance from its more distal portion (PL VIII. fig. 17 ; PI. IX. figs. 14, 15). In G. 

 McCoyi there is a sort of thick rim all round the opening (PI. VIII. fig. 12; PL X. 

 tig. 8) ; this also appears in G. campanulatus (PL X. fig. 10), and is sometimes 

 developed into a thick shield-like process immediately behind the spiracle (PL IX. 

 fig. 8), an indication of which is also seen in G. Derbiensis (PL IX. fig. 5). In some 

 forms of G. Norwoodi the spiracular opening is nearly flush with the general surface 

 of the deltoid and not specially prominent (PL II. figs. 32, 33) ; but in others the 

 margin of the opening is produced upwards into a little tube, as shown in PL II. 

 figs. 34, 35, and PL VII. figs. 5, 6. It is worth notice that the interradials of 

 Cyathocrinus Gilesi are described by Wachsmuth and Springer ' as " each one pro- 

 vided along its upper face with a conspicuous central node." We do not imagine 

 that these nodes were perforated like the spiracular tubercles in G. Norwoodi, as we 

 believe that the respiratory and generative organs of Cyathocrinus were contained, 

 not in the calyx, but in the arms ; but there is a sufficient resemblance between the 

 two structures to make it worth recording. 



The curious genus Hetrrollastus seems to be most nearly allied to Granatocrinus 



in the structure of its spiracles, for the two hydrospire-canals in each interradius lie 



in well-defined grooves on the inner surface of the deltoid ; but they open separately 



at the base of the conical process at its proximal end, as shown in PL VI. figs. 3, 4. 



1 ' Revision of the ralaeoeriuoidea.* I'art III. lbbo, pp. 21, 33, pi. iv. fig-. 2. 



I' 2 



