68 
TH. MORTENSEN, 
(Schwed. Südpolar-Exp. 
Classen u. Ordnungen. Echinodermen. IV. Die Seeigel 1904, p. 1390) makes both 
Tripylus and Abatus synonyms of Hemiaster. 
Though I cannot agree with AGASSIZ in the diagnosis given by him for the 
genus Tripylus , I agree with him in regarding the species excavatus as the type of 
a separate genus, Tripylus , based on the following characters: The anterior lateral 
ambulacra are not petaloid in their whole length from the apex down to the peri- 
petalous fasciole; the 3 — 5 lower plates have only simple pores, a feature reminding- 
one, in fact, somewhat of Agassizia and not found in any of the other South Ame- 
rican forms of the present group. The tubefeet of the odd ambulacrum are very 
small and rather distant, with no distinct rosette plates and a quite rudimentary 
sucking disk. These two characters, together with the well developed latero-anal 
fasciole, evidently justify separating it from Abatus as a distinct genus, which, of 
course, has to keep the name Tripylus Phil.; the name Hamaxitus Tr0SCHEL can 
only be a synonym of Tripylus. All the other species, cavernosus etc., agree in 
having no or only a rudimentary latero-anal fasciole (excepting the young ones); 
the anterior lateral ambulacra are petaloid in their whole extent down to the peri- 
petalous fasciole; the tubefeet of the frontal ambulacrum have a rather well devel- 
oped sucking disk and rosette plates (least so in cordatus and Agassizii). These 
species evidently make a natural group, for which the generic name Abatus Trosch. 
has to be retained. — In the pedicellariæ additional characters for distinguishing these 
two genera are, apparently, not found. Both in Tripylus and Abatus we find a very 
characteristic form of rostrate pedicellariæ (PI XIX Figs. 30, 38), with the blade quite 
open, almost flat, not widened in the point and generally very little bent. Globi- 
ferous pedicellariæ have not been found in Tripylus ; in Abatus they are of the 
Schizaster- type, with interior gland-room, and with 2 — 3 rather long teeth on either 
side of the opening (seldom with only one tooth on either side). 
The species Tripylus Philippii Gray was removed to the genus Schizaster , 
nearest to X. fragilis , by AGASSIZ in the »Revision of Echini» (p. 612) with the re- 
mark that, after it has been shown »that the number of genital openings alone is 
not a suitable generic distinction, and after LüTKEN’s exhaustive comparison and 
analysis of the reasons for uniting T. fragilis to Schizaster, there is no necessity for 
further discussion of the question of the generic affinity of these two species.» * 
I cannot at all agree with AGASSIZ here. As I have shown in the »Ingolf» Echi- 
noidea II. p. 120 — 123, the species hitherto referred to the genus Schizaster form 
* It is not quite correct when it is stated in the »Revision of Echini» (p. 612) that Gray referred 
his species to Tripylus »on the same grounds which induced Sars to refer its northern congener to it», 
viz. the three genital pores. Gray does not give the number of the genital pores as a chief character of 
the genus Tripulus , saying in the diagnosis of the genus »ovarial pores three or four» (Catalogue Rec. 
Ech. p. 58). The character upon which Gray distinguishes the genus Tripylus from Schizaster he expressly 
says to be »the regular cordate form and central vertex» (Op. cit. p. 59). 
