64 
TH. MORTENSEN, 
(Schvved. Südpolar-Exp. 
would even justify making it the type of a separate genus; but since it otherwise 
agrees so closely with the other species I have thought it better to refer it to the 
genus Plexechinus, which represents, in any case, its nearest relation. 
The marked deepening of the anterior ambulacrum and the actinostome is a 
highly interesting feature, pointing distinctly towards the Pourtalesiæ. This species, 
much more than the two other species hitherto known of the genus, tends to mark 
the genus Plexechinus as a connecting link between the Urechinidœ and the Pour- 
talesiidce ; but still the urechinid affinities are the most prominent. (Cf. »Ingolf» 
Echinoidea. II, p. 57—58.) 
Amphisternata. 
Fam. Spatangidæ. 1 2 
The South American Spatangoids of the Abattis- group have a very interesting 
and rather intricate history. The first author to treat of them was Philippi, who in 
1845 in his paper »Beschreibungen einiger neuen Echinodermen, nebst kritischen Be- 
merkungen über einige weniger bekannten Arten» (Arch. f. Naturgesch. XI. 1 p. 344) 
establishes three species, viz. Tripylus excavatus , cavernosus and australis. While 
L. AGASSIZ & Desor in their »Catalogue raisonné des Échinides» (1846) refer Tr. 
excavatus to Agassizia and the two other species to Brissopsis, TROSCHEL goes another 
way, establishing a subgenus, Hamaxitus , for Tr. excavatus and another subgenus, 
Abattis, for cavernosus and australis (»Über die Gattung Tripylus». Arch. f. Natur- 
gesch. 1851). Next Gray in his »Catalogue of the Recent Echinida» (1855) refers 
the two latter species to his genus Faorina , to which genus he likewise refers the 
species antarctica described by him in 1851 (Descriptions of some new genera and 
species of Spatangidæ in the British Museum. Ann. Nat. Hist. 2 Ser. VII. p. 130). 
Later on (1872) A. AGASSIZ in the »Revision of Echini» refers the same two species 
to the genus Hemiaster ( Faorina antarctica being made a synonym of H. caverno- 
sus'), and in the »Hassler»-Echini (1874 p. 20) he points out that H. australis is in 
all probability the young of H. cavernosus. Subsequently, in the »Challenger» Echi- 
noidea (1881 p. 184) Agassiz has come to the conviction that »there seems but 
little doubt the species which have thus far been distinguished as Hemiaster austra- 
lis, Hemiaster philippii 3 and Hemiaster cavernosus are all different stages of growth 
1 On referring the following forms to the family Spatangidæ I wish to state expressly that it is not 
meant as an expression of my views on the classification of the Amphisternata. I hope to be able to set 
forth my views hereon in the Part II of my »Siam-Echinoidea». 
2 Meantime established by Lovén in 1871. 
