Bibliographical Notices. 279 



Messrs. "Wachsmuth and Springer, however, follow Zittel and de 

 Loriol, and regard Pelmatozoa, Urchins, and Stellerids as equivalent 

 classes of Echinoderms, which (as just- remarked) is little more than 

 a nominal change on the classification of forty years ago. 



Following the principles of Burmeister's classification they divide 

 the Pelmatozoa into two subclasses, Anthodiata and Brachiata or 

 true Crinoidea. The first contains the two orders Cystids and 

 Blastoids, while the second falls naturally into Palaeocrinoids and 

 Neocrinoids. There is more to be said for this classification than 

 for that which we have just criticized. But we cannot help thinking 

 that the Cystids and Blastoids are more divergent in character than 

 the Palaeocrinoids and Neocrinoids are, and that, as suggested by 

 Professor Huxley, they deserve to be ranked as classes of Echino- 

 derms equivalent to the Crinoids. This course was taken by the 

 writer in the ' Challenger' Eeport, and has since been adopted by 

 Ludwig, the leading German authority on Echinoderms, who also 

 follows Leuckart, Eay Lankester, and others in giving the Pelma- 

 tozoa the rank of a branch and not merely that of a class of 

 Echinoderms. 



On p. 75 Messrs. "Wachsmuth and Springer profess their inability 

 to point out a single character of either Crinoids, Cystids, or Blas- 

 toids " that is not found exceptionally in one of the other groups." 

 They admit, however, that " probably neither Blastoids or Cystids 

 had appendages united by paired muscular bundles " (p. 78) ; and 

 this is one of the essential characters of the true or brachiate 

 Crinoids. Furthermore, there are at least two strong points of 

 difference which distinguish the Blastoids from the Cystids. The 

 hydrospires of the latter group are very irregularly disposed, while 

 those of the Blastoids are grouped with the utmost regularity in 

 five (or in one genus only four) pairs, which are limited to the radial 

 and deltoid plates and occupy the interradial portions of the calyx, 

 with their slits parallel to the ambulacra ; and the small azygos 

 basal of the Blastoid is always situated in the left anterior inter- 

 radius. In all Palaeocrinoids which resemble the Blastoids in 

 having an unequally tripartite base, with one possible exception, 

 the small plate is in the right anterior interradius ; and we are not 

 aware that any such symmetry is observable in the few Cystidean 

 genera which have only three basal plates, except perhaps in 

 Cryptocrinus cerasus. There are other characters, such as the 

 ambulacral structures of Blastoids, which also differentiate them 

 very clearly from the Crinoids and Cystids. We have yet to become 

 acquainted with any member of the two latter groups which has a 

 Bubambulacral " lancet-plate " like that of the Blastoids. The five 

 lancet-plates of a Pentremite are pierced by longitudinal canals which 

 unite into a circumoral ring, and, as we believe, contained the 

 ambulacral or water-vessels. So far as our present knowledge goes, 

 this subambulacral structure does not occur in any other Pelma- 

 tozoa but the Blastoidea; and despite the number of apparently 

 intermediate forms, we are strongly inclined to think that tlae three 

 groups (Crinoids, Cystids, and Blastoids) are in reality much more 

 distinct than has hitherto been supposed. 



