182 Notices of Memoirs — By Dr, C. Liitken. 



point in the morphology of Echinodermata, I must first confess that 

 hitherto I have been very sceptical as to the theory advocated so very 

 ingeniously by Mr. Billings and now upheld by Mr. Loven. The con- 

 cordance between these two authorities is nevertheless not so great 

 as would be supposed — that the ''pyramid" was the mouth of the 

 Cystidea, and that this orifice accordingly would lie elsewhere than 

 in the centre of the ambulacral system, where it lies in all living 

 Echinoderms and (I may add, where it did lie, I have no doubt, also 

 in the Palaeozoic Crinoids, where no superficial ambulacral channels 

 are to be seen, but where they pursued their way on the inferior 

 surface of the "vault" through the "ambulacral orifices" at the 

 base of the arms, — as shown by Mr. Billings, with whose re- 

 searches [see Decades Geol. Survey of Canada] I was, I regret, un- 

 acquainted when I wrote my paper on Pentacrinus, etc.) I 

 know no other exception to this rule, and would it not be a 

 dangerous thing — not be done without very strong arguments — 

 to give up the leading principle of Palaeontology, viz., that only from 

 the organization of the living form can we learn to understand that of 

 the extinct? Might we not thus too often run the risk of giving 

 up ourselves to the delusions of fancy. When we remember how 

 minute and concealed the mouth often is in recent Crinoids, we 

 should not be puzzled at its being almost or quite invisible in fossils; 

 and if we should search for the interpretation of an orifice, closed by 

 a definite low number of triangular valves, will not several recent 

 Bchinidce {Echinocidaris, Echinometra arhacia ; Leshta itself,) give 

 us the answer, that such an aperture could (at least) be a vent ? Nor 

 can I well conceive that an aperture should altogether fail to exist in 

 the centre of the ambulacral system of Cystidea. How otherwise could 

 the ambulacral vessels communicate with the interior ? And if such 

 an orifice must be assumed (though it be often obliterated and hidden 

 in the fossils), why should not this "apical" or "ambulacral 

 orifice" be also the mouth as in Asteridce and recent Crinoids, and 

 the valvular orifice be the vent, analogous to the "proboscis" of the 

 Palaeolithic Crinoids^ or the "oral tube" of the living? The supe- 

 riority of size of the presumed mouth is not, as Mr. Billings thinks, 

 a very good argument. Has not the oral tube in many of our 

 recent Crinoids {Anteden, Actinometra, Pentacrinus) the same pre- 

 ponderance over the minute buccal orifice ? Nor has the repeated 

 revision of the published descriptions of other Cystidea, accessible to 

 me, convinced me of the correctness of a theory, according to which 

 the mouth would, in many instances, lie very far from the arms, 

 sometimes nearer to the base (the stalk or point of attachment) than 

 to the apex of the calyx. The argument deduced in later times from 

 the presumed existence of five similar peristomatic valves in the 

 recent Pentacrini, I have elsewhere had the opportunity of refuting^; 

 no such hard "clapets" are to be seen in P. Miilleri, and until their 



1 The analogy between the valvular aperture of Caryocrinus and the " proboscis" of 

 Crinoids is also argued by Mr. Billings (Dec. No. p. 1 4. 



' Ora Vestindiens Peutacinen, p. 205 (Vidempel. Meddel. f. d. Naturhist Foreninff, 

 1864). 



