1895. SOME NEW BOOKS. 4 J 7 



cannot in a morphological sense be said to form a part of the calyx 

 or to have anything to do with the apical system of plates. The 

 greater or less extension of the lobes of the chambered organ below 

 the actual limits of the calyx has nothing whatever to do with a 

 centrodorsal, and is of no morphological importance. Such is the 

 conception of the centrodorsal as we receive it from the most eminent 

 writers on the Crinoidea — Wyville Thomson, the two Carpenters, 

 De Loriol, and Ludwig. It is, therefore, incorrect and misleading of 

 Dr. Lang to say (p. 897) that the expanded centrodorsal forms part of 

 the calyx of Apiocrinidae, or (p. 898) that there is a centrodorsal in 

 the calyx of the Bourgueticrinidae. The structure to which he is 

 here alluding is the proximal stem-ossicle, and it is not a centrodorsal 

 in any sense of the term, although that name has occasionally been 

 applied to it by. the compilers of text-books. 



Let me add a word on my own account as to the dorsocentral. 

 Dr. Lang cannot be blamed for considering some plate with this 

 name to be an essential element of the echinoderm apical system, 

 since he is merely following the highest authorities, among whom 

 may be mentioned Loven, P. H. Carpenter, and Sladen. Personally, 

 I have long considered this plate to be, like the now abandoned oro- 

 central, no more than a myth of transcendental morphology. On 

 purely palaeontological grounds, and specially from a consideration of 

 the Cystidea, I have found it impossible to swallow the extended 

 homologies that have been maintained, chiefly by the writers just 

 named, between the apical systems of the various orders of 

 Echinoderma. This, however, is a vast question, only to be settled 

 by reference to decided facts, too many to be dealt with here. But, 

 so far as the dorsocentral is concerned, the following facts may be 

 recalled to mind. In the whole of the Crinoidea, Cystidea, and 

 Blastoidea, the actual existence of such a plate is known only in the 

 embryo Antedon and the adult Uintacrinus and Mavsupites. Indeed, 

 even Mavsupites should probably be set on one side, for it is quite 

 open to us to believe, as Seeliger for one does believe, that the 

 central apical plate of this genus is merely the top segment of a stem, 

 a legacy from stalked ancestors which has become modified and 

 incorporated in the calyx wall. If this plate were a true centro- 

 dorsal, that is, if it bore cirri, the question would be settled ; but the 

 absence of cirri does not necessarily prevent it being derived from 

 one or more stem-ossicles. Unfortunately, in the picture of ancient 

 crinoids that present knowledge permits us to call up, Mavsupites is a 

 kind of Mahomet's coffin hanging between heaven and hell; just as it 

 seems to have no descendant, so also it has no visible ancestry. In 

 this inquiry, then, it offers no evidence worth attention. The plate 

 in Uintacvinus may likewise be a stem-ossicle, or it may represent 

 fused infrabasals. The belief in a crinoid dorsocentral must, there- 

 fore, rest on the facts of development in Antedon. Here it should be 

 remembered that the ascription of this plate to the apical system of 

 the calyx is a pure assumption ; at least, I cannot find that anyone 

 has ever seen it forming a part of the calyx. When it is first seen it 

 is already separated from the calyx by a varying number of 

 columnals, and, at this early period, the basals and orals, which 

 are the only calycal plates yet formed, are still remote from one 

 another and unsymmetrically disposed. There is, in short, no 

 evidence to show that this plate ever lay at the apical pole 

 symmetrically surrounded by the five basals. By those who regard 

 it as a calycal element some weight is attached to its shape and 

 structure, so different from those of the developing columnals. But 



