Genera Pseudopygaulus^ Trachyaster, and Ditremaster. 333 



We do not consider either Trachyaster or Mecaster in the 

 light of genera or subgenera^ and as we have noticed the 

 errors associated with the first-named we place it out of the 

 zoological pale. The whole of the species associated by M. 

 Cotteau with Trachyaster must return into the genus Hemi- 

 aster^ and therefore Hemiaster decipiens^ Dune. & Slad., H. 

 apicalis, Dune. & Slad., H. nobilis, Dune. & Slad., and H. 

 carinatus, Dune. & Slad., 1884, op. cit. p. 198, are the correct 

 generic and specific names. 



III. 



A considerable number of species of Hemiaster which were 

 described by de Loriol, E. Forbes, Taramelli, Talavigne, 

 Bouve, Desor, and ourselves have been relegated to a genus 

 Bitremajter, Munier-Chalmas, 1885, by M. Cotteau in the Pal. 

 Fran^. Ech. terr. :^oc^ne, 1887, p. 411, and Bull. Soc. Zool. de 

 France, 1887, p. 10. M. Cotteau has also placed two species 

 which he had described as Hemiaster in this genus. One 

 would have thought that a new genus which was to alter the 

 classificatory position of some of the best known species of 

 Hemiaster^ and which by so doing conveyed a kind of stigma 

 upon some experienced echinodermatists, would have been 

 well placed before the biological world, published and fully 

 illustrated, and that the essay would be accompanied by 

 remarks explanatory of the reasons for antagonizing the 

 opinions of Forbes and de Loriol. Moreover one would have 

 thought that the description and argument would have been 

 so well circulated that the students of the recent fauna might 

 be informed concerning the new genus. We had much search 

 after the new genus, and at last found it in Comptes Rendus 

 Acad. Sci. 2 semestre, 1885, p. 1076, under the heading of 

 " Distribution of genital openings " : — " Genera with only 

 two genital pores. — Ditremaster. Hemiaster 7iiix, which occurs 

 in the Middle Eocene of the Alps, and which has always 

 been accorded four pores, has really only two, situated in the 

 posterior genital plates. //. Covazii, from the same forma- 

 tion in Istiia, has the same number. It is probable that a 

 great part, if not the whole, of the Eocene Hemiasters should 

 be referred to Ditremaster.^'' This is all. 



There is not a single word of reference added upon the very 

 considerable literature upon the subject of the species of Hemi- 

 aster w'lih. three and two genital pores, and Tripylus and Abatus 

 are left out. There is no reference made to the Paloiostoma- 

 question or to that of the Hemiasters with two pores, by de 

 Loriol and ourselves (see ' Palseontographica/ xxx. 1881, 



