50 CATALOGUE OF THE BLASTOIDEA. 



also seems to present itself in M esob t 'a st us Sower byi and in M. elongatus (PI. VI. fig. 13 ; 

 PI. XI. fig. 15), though the markings on the upper surface of the hydrospire-plate have 

 heen worn away in our specimens. The difference between the well-defined hydrospire- 

 plates in the genera above mentioned and the under lancet-plate of Pentremites is very 

 evident. The former belong to the sides of the ambulacra and do not meet beneath 

 its middle line, where a more or less wide gap is left between them, leading down into 

 the interior of the calyx (PI. X. figs. 11-14 ; PL XL figs. 11-15). The under lancet- 

 plate of Pentremites and Orojrfiocrinus, however, occupies the middle of the radial sinus, 

 and may or may not reach its edge (PI. I. fig. 7 ; PL XII. figs. 13, 1G ; PL XV. figs. 4, 

 10, 13). Its distinctness from the inner walls of the hydrospire-sacs is well shown 

 in Orophocrinus pentangularis, where it is partly broken away, and is seen to be 

 resting upon the truncated edges of the two walls in question (PL XV. fig. 10). 



The under lancet-plate in these two types is not therefore, as Hambach 1 has asserted, 

 " the upper blade of the hydrospiric sac, which is smooth, and overlays the plicas." 

 He says that this " may mislead to the supposition of having here a sublancet-plate." 

 So far as regards Granatocrinus, we are quite in accordance with him upon this point, 

 having described the hydrospire-plate two years before he noticed it ; but at the same 

 time we expressly stated that this genus had no under lancet-plate, mentioning also 

 that we could confirm Wachsmuth and Springer's discovery of an under lancet-plate 

 in Pentremites, and that we had likewise found it in Oropfiocriims 2 . Hambach's 

 attempts to explain it away were therefore not wanted for Granatocrinus, in which 

 genus it has never been described, while, as shown above, they do not suit the con- 

 ditions of its occurrence in Pentremites and Orophocrinus. 



Reference has already been made to the very general, if not universal, presence of 

 a canal within the lancet-piece of a Blastoid. It was first seen, though misinterpreted, 

 in Granatocrinus elliptieusby the late Mr. J. Rofe 3 , who figured it as seen in section in 

 the original of our PI. X. fig. 13. But finding a large number of weathered specimens, 

 like that represented on PI. VIII. fig. 20, he was led to suppose that this lancet-plate 

 " is in reality a compound plate formed of two contiguous plates," each of which is inter- 

 radial in position, and goes to form the lancet-plates of two ambulacra ; and he 

 described how in many weathered specimens these two parts " appear to meet only at 

 the top and bottom of the cross section, leaving a lozenge-shaped opening between 

 them," as shown in the figure (PL X. fig. 13). We now know that this opening is the 

 transverse section of the internal canal, the existence of which was first noticed by 

 Hambach. But this author, in claiming the priority of his discovery 4 , is somewhat 

 unjust to Rofe when he says, " That the lancet-piece is perforated by a very fine canal 

 through the centre, in its whole length, was, so far as I know, first described by me, 



1 Trans. St. Louis Acad. Sci. 1884, vol. iv. no. 3, p. 538. 



2 Ann. & Mag. Nat. Hist. 1882, vol. ix. pp. 215, 217, 218. 



3 Geol. Mag. 1805, vol. ii. p. 249, pi. viii. fig. 7. 



* Trans. St. Louis Acad. Sci. 18S4, vol. iv. no. 3, p. 537. 



