334 Messrs. Duncan and Sladen^s Objections to the 



and Ann. & Mag. Nat. Hist. 1884, xiv. p. 225) . There is no 

 reference to A. Agassiz's work in the ' Challenger ' Report, 

 and even M. Pomel is not noticed and his Hemiaster-g&aws, 

 with only two pores — Opissaster {op. cit. p. 37) — is passed 

 bj. 



M. Cotteau, in Pal. FranQ. 1887, Ech. terr. :^oc^ne, p. 411, 

 accepted this genus Ditremaster and attempted to improve it. 

 It will be found that it is not such a simple genus as one might 

 have expected, and M. Cotteau places as synonyms Hemiaster 

 (pars) and Trachyaster (pars). 



It appears that the reason of Trachyaster being in relation 

 to Ditremaster must be from M. Pomel having jumbled up 

 species of Hemiaster with two pores with those which have 

 four, the niadreporite in both instances passing backwards 

 and separating the posterior ocular (radial) plates. This is 

 satisfactory, because it indicates that Trachyaster ^ Pomel, is 

 of no value. Having enlarged the diagnosis of Ditremaster^ 

 M. Cotteau altered the generic titles of the Herniasters 

 already referred to. The recent species appear to have 

 escaped the memory of the distinguished palaeontologist, 

 and he has also neglected to I'cfer to previous writers upon 

 the subject. Otherwise he would not have altered the generic 

 title of de Loriol's species ; and we must believe that had he 

 read our essay upon Hemiaster elongatus^ which has two geni- 

 tal pores, he would have paid us the compliment of debating 

 the matter. M. Cotteau must be aware of Prof. Sven Loven's 

 work upon the Ethmolysian Herniasters^ and it is incon- 

 ceivable that with all M. Cotteau^'s great experience, un- 

 equalled we might say, he should alter tlie generic title of 

 species upon such slight foundation. In his first definition of 

 Hemiaster^ 1847, Desor made no reference to the number of 

 genital pores or to the extension of the madreporite; and in our 

 " Fossil Echinoidea of Sind, Kach, and Kattywar," in Pal. 

 Ind. ser. xiv., we followed his example, and for the same 

 reason that made that authority neglect the very variable 

 characters — the number of pores and the extension of the 

 madreporite. We have enlarged upon the distribution of 

 these structures in other genera in a former page, and it is 

 only necessary to refer to de Loriol, who considers that these 

 species of Hemiaster with a smaller number of genital pores 

 than the old Cretaceous types are members of a group of the 

 genus. No one would classify these neonomous Ethmo- 

 lysii, to use Lovdn's terminology, with the archeeonomous 

 ethmophract species ; but they are still Herniasters^ for all 

 the other characters are the same. To that opinion we adhere. 

 It is necessary to point out that in the recent species Henii- 



