THE ECHINOIDEA. 
Bd. VI: 4) 
67 
fasciole is present, at least in the young, while in Hemiaster such a fasciole is never 
developed.) 
The genus Tripylus was established by Philippi (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 »Über 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 : »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 {grandis 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 PlIIL. and Philippii 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 »Schizaster 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 Delage & HÉROUARD in their »Traité 
de Zoologie concrète. III. Echinodermes. 1903, p. 271), while MEISSNER (Bronn. 
