248 MR. A. J. JUKES-BROWNE ON HOLASTER ALTUS. [Aug. 1 898, 



passent aux autres. Je commeiice a croire que, lorsqii'on connaitra 

 bien VHol. Bischqffi, par "une serie un peu nombreuse d'exemplaires, 

 efc qu'on aura pu etudier le test qui manque toujours, on arrivera 

 probablement a reunir VHol. Bischoffi, a VHol. alius. Dans I'etat 

 actuel des choses, je crois qu'il sera preferable de nommer votre 

 espece Holaster alius. Ces Holaster sont difficiles a bien demeler, 

 offrant certains passages ; ainsi vos trois premiers [de Wilmington] 

 ressemblent a une variete de VHol. suhglobosus que j'ai fait figurer.' 



Two specimens from Beer Head had previously been sent to 

 M. Gauthier, of Sens, who considered them to be Holaster alius, 

 and wrote that most authors regarded this form as only a variety of 

 H. suhglobosus, but that M. Bucaille, after having changed his mind 

 several times, had ended by re-establishing H. alius as a distinct 

 species in his ' Etudes sur des Echin. foss. du Departement de la 

 Seine Inferieure,' p. 6, pi. v. 



Having had the opportunity of examining upwards of sixty 

 specimens from Wilmington, and about twenty from the coast- 

 sections, I am not surprised at the doubts of M. Bucaille, and am 

 convinced that the anticipation of M. de Loriol-Lefort as to the 

 union of H. Bisclioffi with H. alius will prove correct. So far 

 as I am able to judge, there is among the Devon specimens every 

 gradation from a form which cannot be distiuguished from H. 

 Bischoffi^ through forms which are undoubtedly identical with 

 French specimens of H. alius, to one which, if found alone, would 

 be regarded as a rather small and well-marked variety of H. suh- 

 globosus. 



It is a curious fact, however, that I have not seen a typical 

 H. suhglobosus among all those from the calcareous sand of 

 Wilmington which have passed through my hands, although I have 

 two from the overlying bed which, though small, certainly belong 

 to that species. 



The impression that one receives from an examination of a large 

 number of these Holasters is that one is looking on at the actual 

 process of the evolution of a new species ; for, in this area at any 

 rate, the Bischoffi-tyipe seems to be the oldest ; on the coast it is 

 most abundant in the bed numbered 10 by Mr. Meyer and in the 

 lower part of his No. 11, where it is accompanied by the aZ^ws-type 

 and its varieties, while in the upper part of 11 true suhglobosus 

 occurs occasionally ; lastly, in No. 12 typical suhglobosus occurs 

 without the others. At Wilmington the aZ^w^-type prevails, and 

 seems to be throwing out varieties which are broader, lower, 

 and larger, and which are gradually developing into the form which 

 we know as H. suhglobosus. 



If this view be correct, it is unfortunate that the form last 

 evolved should have been the first described, and that our laws of 

 nomenclature require that the earlier form should be placed as 

 a variety of the later one. Perhaps, in spite of the preservation of 

 the intermediate forms, it will be more convenient to regard the one 

 extreme (whether it be called alius or Bisclioffi) as having an equal 

 right to be called a species as the other extreme (suhglobosus) ; for 

 if these intermediate forms had been all destroyed, I think that 



