the Morjihology oj the Blastoidea. . 217 



what we liave seen we think it possible tliat the hydrosplral 

 tubes may be continued onto the ends of the ambuUxcra actu- 

 ally within the substance of the radial plates. This is at any 

 rate the case tlu'oughout the greater part of the length of the 

 ambulacra of Triccelocrinus^ as we have found from sections of 

 1\ Wood/nani, and from the examination of some large 

 isolated radials Avhich may, we think, possibly belong to T. 

 ohh'quatus, Eomer, sp. We take this species to be an en- 

 tirely different one from that which was described later by 

 Meek and Worthen under the same name. 



Some valuable observations have been recently made by 

 Messrs. Wachsmuth and Springer*, and by Dr. Hambachf, 

 on the structure of the ambulacra of the Blastoids. This is 

 more especially the case with regard to the subambulacral 

 canals, which were first discovered by Rofe in Oranatocrlnus 

 eJUpticus^ although their true nature was misinter})reted by 

 him ; for he believed the lancet-plate of this type (then re- 

 ferred to Pentremites) to consist of two lateral halves. As 

 Hambach has pointed out with respect to other sjjecies, this 

 does sometimes appear to be the case in worn specimens ; for 

 when the superficial portion of an ambulacrum has been re- 

 moved the canal within the lancet-piece (which was seen, 

 though misinterpreted, by llofe) is not unfrcquently exposed. 

 We have had the advantage of examining the whole of Mr. 

 Rofe's collection, together with many specimens of Granato- 

 crinus Noriooodi] and we are convinced that in Qranato- 

 criims, as we define the genus |, there is but one subam- 

 bulacral plate, the lancet-jjlate, which is pierced by a 

 longitudinal canal. Messrs. Wachsmuth and Springer §, 

 however, have described and figured the lancet-plate of Pen- 

 tremites as imperforate, but as resting on an underlancet-plate 

 which encloses a canal. Hambach ||, on the other hand, de- 

 scribes the lancet-plate of typical Pentremites (P.Jloreah's, P. 

 sulcatus, P. pyriforrnis, &c.) as "pierced through the centre, 

 in its whole length, by a very fine canal;" and we are in- 

 clined to think that he is right. 



For although we agree with Wachsmuth and S])ringcr in 

 finding two subamulacral pieces in Pentreiniies, it seems to us 

 more probable that the canal should be in the upper or lancet- 



* " Revision of the Pala}ocnnoidoa.— Parts i., ii.," Proc. Pliilad. Acad. 

 187U, 1881. 



•j- " Contributious to the Auatoiiiy oftlie (ieuus Penfrani/es, witli De- 

 scriptions of new Species," Trans. St. Louis Acad. vol. iv. nn. 1, pp. l4o 

 IGO. 



X Seejws^m. 



§ Kevision, part i. pi. iii. tig. 5. Il Loc, cU, p 14'. >. 



