THE AMBULACRA. 17 



tremites pyrtfbrmis may be the duct or vessel described by Hambach in the same 



position. But \vc are inclined to doubt this Cor various reasons; and we think it Gar 

 more probable either that Wachsmuth and Springer have really seen the canal within 

 the lancet-piece, but in a position rather nearer the dorsal surface than it often occupies, 

 or that the passage which they describe within the inner lancet-piece is merely the 

 median groove upon its upper surface, as shown in our figures (l'l. XII. figs. 1!, L6), 

 and that all the calcareous tissue above this really belongs to the lancet-piece. Hut 

 we have no doubt that they are right in noting the presence of an under lancet- 

 piece. Hambach 1 says, however, that he must deny its existence, ••and would 

 advise Mr. Carpenter, before making such assertions, to examine the matter more 

 carefully ; for the truth of the matter is, that there is no such thing as a sublancet 

 plate, and what has been taken for it is only the upper blade of the hydrospiric sac, or 

 the calcareous substance from the duct above it ; because immediately under the 

 lancet plate lies a duct or vessel (as already described in my paper), and under this 

 the hydrospiric sac. I hardly deem it necessary to give a definition of the difference 

 between the above-named organ and a sublancet plate, which latter could only mean 

 a something like the lancet plate, only underlying it." 



This, however, is precisely the meaning which we intended to convey with regard 

 to the under lancet-plate of Orophocrinus and Pentremites, the only two genera in 

 which we have noted its presence. Hambach's denial of its existence, although 

 couched in very general terms, is perhaps not meant to apply to Orophocrinus, as he 

 only professes to be writing about " the Pentremites." At any rate we do not think 

 that our statement will be questioned by those who examine our figures of it in 

 0. verus, 0. pentangularis, and 0. stelliformis (PI. XV. figs. 4, 10, 13). In the last- 

 named species it forms a sort of shallow trough in which the lancet-piece lies ; and 

 it meets the sides of the radial sinus immediately beyond the radio-deltoid suture, so 

 that the hydrospire-clefts of other Blastoids are here reduced to the short and linear 

 spiracular openings at the proximal ends of the ambulacra. These are rather short 

 in the specimen represented in PI. XI. fig. 9 and in PL XV. tig. 13; and they 

 appear still shorter in the latter figure, owing to the position in which the ambulacrum 

 is drawn. The proximal end of the under lancet-plate is not seen, as it is conceal* d 

 beneath that of the broken-lancet piece, but its relations are very well shown in a 

 specimen of Orophocrinus verus (PI. XV. fig. 4). One ambulacrum has lost the whole 

 of the lancet-plate except its distal end, so that the relations of the under lancet-plate to 

 the deltoids and to the ambulacral opening are very well seen. This opening is not 

 situated entirely between the deltoid pieces as in Pentremites pyriformis (l'l. I. figs. 6, 

 7; PI. XII. fig. 13), but its hinder border is formed by the under lancet-plate, just as 

 is figured by Wachsmuth and Springer 2 in their general diagram of a I'culrnnifi s. 

 The proximal end of the under lancet-plate is more deeply hollowed than the distal 



1 Trans. St. Louis Acad. 1884, vol. iv. no. 3, p. '>:'<<. 

 - •■ Revision of the Palaeocrinoidea," Ft. I. pi. iii. fig. 4. 



