186 p. HERBERT CARPENTER. 



For if they do functionally represent the sand canals of the 

 other EchinodermSj'hvhy do they coexist with the sand canal 

 in the Ophiurids ? Whatever their nature, however, they 

 were present in Actiiiocriiitis , but greatly reduced in number. 

 In both Antedon and Actinometra they are extensively deve- 

 loped ; but Ludwig has found that in Rhizocrinus^ there is 

 but one in each interradius, and I imagine that this was also 

 the case in Actmocrinus. 



From what has been said above, it will be evident that 

 I entirely accept Schultze's hypothesis of a subtegminal 

 mouth in the PaI(2ocrmoidea, which has been attacked 

 by Billings/ but ably defended by Wyville Thomson/ 

 Liitken,^ Meek and Worthen/ and lastly, by Wachsmuth.^ 

 The last mentioned observer says that " The little central 

 aperture located at the upper end of the vertical axis, 

 occupied on the casts, and hence below the vault of these 

 Crinoids, exactly the same position that the internal mouth 

 of Antedon, occupies at the peristome, while the position of 

 the string-like ridges (in case they represent passages, as I 

 can hardly doubt) is analogous with that of the open food 

 grooves of recent Crinoids/' I cannot but believe that 

 Wachsmuth^s explanation of these ridges is the true one, 

 though it is by no means necessary that they should repre- 

 sent closed passages. In many recent Comatulce it is ex- 

 ceedingly common for the ambulacral grooves of the disc to 

 be considerably raised above the interambulacral areas, so 

 as to present an appearance of '' elevated rounded ridges 

 almost like strings overlying the surface," just as Wach- 

 smuth describes in his casts. 



Billings' objections to the theory of a subtegminal mouth 

 in the Palceocrinoidea, appear to me to be the result of a 

 confusion of terms, and of a want of acquaintance with the 

 anatomy of recent Crinoids. In the first place he described 

 two quite distinct and separate structures under the single 

 name of " ambulacral groove." On p. 20 of the Decade, he 

 used this term in the sense in which it was used by Miiller, 

 namely, to denote the furrows radiating outwards from the 



' Loc. cit., p. 118. 



- " Notes ou the Structure of the Crinoida, Cystidea, and Blastoida," 

 'Canadian Naturalist/ 1869, pp. 277—283, and 1870, pp. 191—198. 



3 "On tlie Structure of the Palaeozoic Crinoids," 'Nature/ vol. iv, 

 pp. 496—497. 



^ "Notes on Loven's Articles on Leskia mirabilis and on Hypotiome 

 Sarsii" ' Canadian Naturalist,' 1868, pp. 439—441, and 1869, pp. 267— 

 269. 



* Loc. cit., pp. 441 — 446. 



6 Loc. cit., pp. 116—120. 



