Bd. VI: 4) THE ECHINOIDEA. 67 



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

 developed.) 



The genus Tripylus was established by PlllLIPPI (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 

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

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

 Fauna II. p. 62). TROSCHEL in his paper -Tiber die Gattung Tripylus> p. 72, after 

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

 and Agassizia in AGASSIZ cS: Desor's »Catalogue raisonne des Echinides* gave the 

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

 ambulacris profundatis, anterioribus subtransversis; polo dorsali subcentrali; poris 

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

 cludente.) He further distinguishes the three subgenera Hamaxitus (excavatus), 

 Atrapus (graudis TROSCH.) and Abatus (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 Hemiaster, representing the -^Schizastcr type* 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. — DUNCAN (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 Hemi- 

 aster, and the same course is followed by Dei.AGE & Herouard in their »Traite 

 de Zoologie concrete. III. Echinodermes. 1903, p. 271), while MEISSNER (Bronn. 



