82 PROCEEDINGS OF THE ACADEMY OF [1887. 



THE SUMMIT PLATES IN BLASTOIDS, CEINOIDS, AND CYSTIDS, AND 

 THEIR MORPHOLOGICAL RELATIONS. 



BY CHARLES WACHSMUTH AND FRANK SPRINGER. 



Messrs. Robert Etheridge Jan. and Dr. P. Herbert Carpenter, 

 have recently published, under the auspices of the Trustees of the 

 British Museum, a most important and valuable contribution to 

 palaeontological research, in the form of a memoir, which is in 

 effect a Monograpli of the British Blastoids.* The work is marked 

 by a thoroughness and wealth of illustration, characteristic of the 

 scientific publications on special subjects issued under the patronage 

 of the British Goverment, which makes us wish that the facilities 

 offered by our own government in that direction might be a little 

 more extensive. The high reputation of the authors is such an 

 ample guarantee of scientific excellence in the execution of the 

 work, that it is scarcely necessary to do more than allude to the 

 fact of its appearence. The points as to which we should venture 

 to differ with the authors are but few; upon these, however, we 

 regret we find ourselves materially at variance with their views. 



The whole of chapter IV, from p. 66 to 74 inclusive, is devoted 

 to a discussion of the summit plates and their morphological 

 relations. The authors undertake to prove that while the summit 

 plates in the Blastoids do not present, as a rule, any very definite 

 arrangement (p. 118), yet they exhibit a series of variations in 

 number and position, in some degree corresponding with a similar 

 but more extensive series of variations among the Palaeocrinoidea; 

 that both exhibit a transition from five closely united plates fully 

 covering the summit, to a set of six proximal plates surrounding a 

 central one. The six proximal plates are held by them to be the 

 homologues of the five oral plates of the xsTeocrinoidea a theory to 

 which the division of the proximals into six or more has always 

 interposed a very serious difficulty. If such a transition from five 

 closely fitted plates to six or more around another could be 

 established, of course its tendency would be to diminish the diffi- 



*Catalogue of the Blastoidea in the Geological Department of the British 

 Museum (Natural History), with an Account of the Morphology and Systematic 

 Position of the Group, and a Revision of the Genera and Species, By Robert 

 Etheridge Jun. and P. Herbert Carpenter, D. Sc, F. R. S., P. L. S.-4 to.-Pp. I- 

 XVI, 1-322; 20 plates. London. Printed by order of the Trustees, 1886. 



