95 



III all the species above cited, the figures (with the exception of 

 <7. ornatiis) exhibit the relative position of the mouth and radial centre, 

 as it has been actually seen in casts of the interior of the vault. But 

 besides these, numerous examples may be found in the works of Miller, 

 Austin, De Koninck, Phillips, Meek, Worthen, Shumard, Hall, Lyon, 

 Cassaday and others, of Crinoids whose external characters show that, 

 in them, the mouth cannot be in the central point from which the grooves 

 radiate. 



■ With respect to Prof. Thompson's theory, I freely admit that if it is 

 true that in all the Echinoderraata, fossil and recent, the mouth is the 

 radial centre, then, that aperture must be the one which I call the 

 ambulacral orifice in the Cystidea. The views, however, advocated by 

 me in my Decade No. 3, appear to be gradually gaining ground. As 

 these fossils are rare, few have occasion to study them, and consequently 

 the subject has not been much discussed since 1858, the date of the 

 publication of that work. The following are the only authors, so far 

 as I have ascertained,who have given their opinions on this vexed question 

 during the last eleven years : — 



Prof. Wyville Thompson, op. cit., p. Ill (1861), agrees with me that 

 the lateral aperture is not an ovarian orifice, but, as we have seen, is 

 strongly opposed to the view that it is the mouth. lie calls it the anus. 



Prof. Dana (Man. Geol., p. 162, 1863) recognizes it as the homologue 

 of the simple aperture (oral and anal) in the summit of those Crinoids 

 which have but one. This is exactly my view. [J. W. Salter agrees 

 -with Prof. Thompson that it is the anus, not the ovarian aperture. 

 (Mem. Geol. Sur. G. B., vol., iii, p. 286, 1866.) Prof. S. Loven of 

 Stockholm has described, in the " Proceedings of the Royal Swedish 

 Academy," 1867, the remarkable sea-urchin, Lcshia mirahUis (Gray), 

 which has the mouth constructed on the same plan as that of the Cystidea, 

 that is to say, with five triangular valve-like phtes, which are immediately 

 attached to the interambulacral plates, without the intervention of a 

 baccal membrane. After comparing this structure with the valvular 

 orifice of SplicBronites j}omnm (Gyll.) he says, " that the * pyramid,* 

 which in Lcshia is the armature and covering of the mouth, is the same 

 thing in the Cystidea is now quite certain ; in the last-named group it was, 

 doubtless, also the vent. The mouth does not lie where J. Muller and 

 Volborth sought for it, viz : in the centre of the ambulacral furrows ; 

 and the organ, interpreted as the vent by Volborth and von Buch, is 

 more correctly regarded as an external sexual organ." Geol. Mag., 

 vol. V, p. 181, Dr. Lutken's trans.] 



