Bd. VI: 4) THE ECHINOIDEA. 6^ 



fasciole is present, at least in the young, while in fleuiiaster such a fasciole is never 

 developed.) 



The genus Tripylus was established by PiliUPPl (Op. cit.); though not definitely 

 diagnosed, it is stated to be based on the single character of having only 3 genital 

 openings. This is certainly an insufficient character, and upon this ground also 

 Brisaster fragilis and allied species would have to be referred to the same genus, 

 as was, indeed, — and thus far correctly — done by M. Sars (Middelhavets Littoral- 

 Fauna II. p. 62). Troschel in his paper sÜber die Gattung Tripylus» p. 72, after 

 justly criticizing the reference of Philippi's three species to the genera Brissopsis 

 and Agassizia in AgaSSIZ & Desor's »Catalogue raisonné des Échinides» gave the 

 following diagnosis of the genus Tripylus: iTesta cordata, suborbiculari, convexa; 

 ambulacris profundatis, anterioribus subtransversis; polo dorsali subcentrali; poris 

 genitalibus tribus (antico sinistro, posticis sinistro et dextro); semita ambulacra in- 

 cludente.s He further distinguishes the three subgenera Hainaxitus (excavatiis), 

 Atrapus {grandis Trosch.) and Abatits {cavernosus, australis) alone by the different 

 development of the latero-anal fasciole: complete in the first, incomplete in the se- 

 cond and wholly wanting in the third. Gray (Catalogue of Recent Echinida 1855, 

 p. 58) gave the following diagnosis of the genus: »Shell cordate, rather depressed; 

 tubercles equal; apex central; ambulacra sunken; the lateral radiating, the anterior 

 pair elongated, the hinder pair short; the odd anterior one deep, forming a distinct 

 anterior groove, with a series of small double pores on each side; surrounded by a 

 very flexuous peripetalous fasciole, with a lateral fasciole separating from it and de- 

 scending under the vent; ovarial pores three or four.» In the genus thus diagnosed 

 he includes the species excavatus Phil. and Pliilippii Gray. In the »Revision of 

 Echini» AgaSSIZ confines the genus Tripylus to include only the species excavatus 

 Phil., giving this diagnosis (p. 588): >Test depressed heart-shaped; apical system 

 anterior; lateral ambulacra sunken; anterior groove slight. Actinal side flat. Peri- 

 petalous fasciole, with continuous lateral and anal fasciole.» (It is regarded as a sub- 

 genus of Hcmiaster, representing the -iSchisaster tj'pe» of that genus.) I do not find 

 in this diagnosis a single really characteristic feature; one of the characters men- 

 tioned, »apical system anterior«, evidently would be of importance, if it were correct 



— but it is not. The apical system is central — as stated by TrOSCHEL and Gray 



— sometimes perhaps slightly anterior, sometimes slightly posterior, but so little 

 that the only correct thing is to say, it is central. — Du^"CAN (Revision of the Ge- 

 nera and great Groups of Echinoidea. Journ. Linn. Soc. Zoology. XVIII. 1889, 

 p. 231) places Tripylus (including Abatus as a synonym) as a subgenus of Hcnii- 

 aster, and the same course is followed by Delage & HÉROUARD in their »Traité 

 de Zoologie concrete. III. Échinodermes. 1903, p. 271), while Meis.SNER (Bronn. 



