68 TH. MORTENSEN, (Schwed. Siidpolar-Exp. 



Classen u. Ordnungen. Echinodermen. IV. Die Seeigel 1904, p. 1390) makes both 

 Tripylus and Abatits 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 TROSCHEL can 

 only be a synonym of Tripylus. All the other species, cavernosas 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 pedicellariae additional characters for distinguishing these 

 two genera are, apparently, not found. Both in Tripyhts and Abatus we find a very 

 characteristic form of rostrate pedicellariae (PI XIX Figs. 30, 38), with the blade quite 

 open, almost flat, not widened in the point and generally very little bent. Globi- 

 ferous pedicellariae have not been found in Tripylus; in Abatus they are of the 

 Sc/tizaster-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 Sc/iizaster, 

 nearest to S. fragilis, by Agassiz in the ^Revision of Echini? (p. 612) with there- 

 mark that, after it has been shown ^that the number of genital openings alone is 

 not a suitable generic distinction, and after Lutken'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 Scliizaster form 



* It is not quite correct when it is stated in the >Revision of Echini* (p. 612) that Gray referred 

 his species to Tripyhts »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 Tripttlus, 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 Tripyhts from Schizaster he expressly 

 says to be »the regular cordate form and central vertex* (Op. cit. p. 59). 



