ARCHAEOCIDARIS. 257 



sociated plates and spines. Such are most unsatisfactory, often difficult to distinguish, and 

 doubtless there are too many recognized species, of little interest except as expressing the geo- 

 graphical distribution of the genus. With available material the best way, it seems, is to group 

 the species on the basis of spine characters, associating those species that have smooth spin.--, 

 those in which the spines bear low nodose spinules, and those with spinules more elevated and 

 directed at right angles to the shaft of the spine, or pointing distally, or spines with lateral 

 flanges, spines triangular in section, or spines inflated. This has at least some resemblance 

 to a natural classification. The type species, as indicated by Bather (1907, p. 453), is A. 

 urii (Fleming) from the Lower Carboniferous of Europe. 



The genus Archaeocidaris is structurally closely related to the Cidaridae, but is n ion- 

 complex in that there are four columns of plates in an interambulacral area instead of two 

 columns. Archaeocidaris may be derived from some early cidarid, perhaps Devonian or Silurian. 

 The fact that I describe a true cidarid (Mioddaris cannoni) from the Lower Carboniferous, 

 which is geologically as early as any species of Archaeocidaris known lends weight to this 

 argument. (See pp. 70, 77, 80, 184, 223, 361, 363.) 



Lambert and Thiery (1910, pp. 124, 125) under what I consider as Archaeocidaris recognize 

 two genera, Archaeocidaris, which they say has interambulacra formed of from five to eight 

 columns of plates, and Cidarotropus, in which they say that the interambulacra are formed of 

 four columns of plates. I know, no species of Archaeocidaris with more than four columns of 

 plates in an interambulacral area, and many of the species which they list in one of their two 

 definite genera are known only fragmentarily from isolated plates so that the number of columns 

 in an area is quite unknown. 



The proper name to apply to this genus is open to question. As shown positively by my 

 friend, Dr. Bather, on the basis of priority, Echinocrinus is the correct name. Thi- name, 

 however, is misleading, was based by Professor Agassiz on a misconception of affinities, and has 

 been abandoned for some sixty years in favor of the entirely appropriate Archaeocidaris of 

 M 'Coy. It is not a case of Archaeocidaris being preoccupied but simply of priority. To revive 

 the old name, Echinocrinus, in accordance with rules of nomenclature, will make confusion at 

 present and in future, and no gain to any one. 



As Dr. Bather justly says (1909a, p. 264), "While there can be no doubt as to the conse- 

 quences of the rules, this seems to me just one of those cases that should be settled by a properly 

 constituted authority in defiance of the rules." Such being the case, pending the action of 

 some formal authority, I feel it best to follow the conservative action of retaining the entirely 

 satisfactory and thoroughly established name Archaeocidaris. The name Palaeocidaris Agassiz 

 and Desor is a pure synonym, Cidarotropus Pomel with Archaeocidaris wotfheni Hall as the 

 type, and Permocidaris Lambert with Archaeocidaris forbesiana (Koninck) as the type, I do 

 not recognize as distinct genera. 



