Herbert L. Hawkins — Studies on the Echinoidea,etc. 161 



Echinoidea covered by my researches are so various that some 

 sections will be independent, in all but their ultimate aim, of the 

 actual order Holectypoida. Much of the work is concerned with 

 recent forms (partly with their histology), some deals entirely with 

 fossil genera aud species, and some is largely stratigraphical in 

 treatment. It is obvious that such diverse sections will affect 

 workers in very different spheres, who will not wish to be burdened 

 with a cumbrous mass of details which have no direct bearing on 

 their particular branch of study. Glory and honour accrue to the 

 author of a massive tome, but understanding and gratitude are the 

 reward of the writer of pamphlets. 



As far as possible it is intended that the earlier sections of the 

 work shall deal with matters of fact and observation, so that the 

 theoretical conclusions derived from them may be concentrated into 

 the later parts, and be more or less synchronous in their appearance 

 and homotaxiai in their expression. I hope to publish the shorter 

 sections (or those of them that deal with subjects of a palaeontological 

 or geological character) in this Magazine, in continuation of the 

 earlier series, most of which appeared here. Larger, or purely 

 zoological, sections will necessarily demand a different environment. 

 Unlike serial publications in the domain of fiction, each part will aim 

 at being complete in itself, in the light of its predecessors, for, in the 

 world as at present constituted, it is a rash, if not a provocative, 

 prophecy to announce that any form of activity will be " continued 

 in our next". 



I. Systematic Discussion - of the genera Ptgaster, Agassiz, and 

 Plesiechinus, Pomel. 

 1. Introduction. 

 The conservatism of the Holectypoida, and in particular of the 

 family Pygasteridae, while rendering the order a favourable group 

 for phylogenetic study, has been a condition contributory to the 

 utmost systematic confusion. It is to be hoped that there are few 

 orders, so small numerically, whose nomenclature is so involved. 

 To a considerable extent the lamentable taxonomic chaos into which 

 the family has fallen, is due to the two common causes of such 

 a state — inadequate description and erroneous identification of 

 species. Other preventable errors have been numerous, but the root 

 of the trouble is buried in the nature of the family itself. "Where 

 evolution is almost stagnant, even generic differences will be slow to 

 appear and indistinct in their early stages ; specific characters must 

 be still less clearly defined. In default of any striking features by 

 which to diagnose their types, authors have tended to use as specific 

 criteria such variations of form and detail as would be considered 

 unworthy of more than passing reference in more plastic groups. 

 Finally, when there is added to these difficulties the fact that the 

 genotype of Pyg aster was subsequently degraded to the position of 

 a synonym, and, when revived, imagined to be a form from a totally 

 different horizon, and belonging to a different section of the family, 

 it will be realized that a systematic revision of that genus is 

 a necessary preliminary to any morphological study of its species. 



DECADE VI. — VOL. IV. — NO. IV. 11 



