Bd. VI: 4) 
THE ECHINOIDEA. 
73 
tinct, though generally less prominent than in the threevalved specimens. The neck 
s well developed, in the larger specimens shorter; the stalk is simple. Quite small 
pedicellariæ of this form might equally well be taken to represent the triphyllous 
form; there is no character distinguishing them definitely from the smaller tri- 
dentate pedicellariæ (PI. XIX. Figs. 36, 43). 
The colour is stated by Philippi to be white; this, evidently, depends on the 
preservation. Most of the specimens seen by me are brownish, generally rather 
dark, both test and spines; a few of them are dark-violet. 
On many of the specimens is found a parasitic or commensalistic Bivalve Mol- 
lusc, which, as I am informed by Mr. H. LYNGE, belongs to the genus Lepton. 
The specimen figured in PI. X. 13 shows several samples of these Molluscs on the 
abactinal side. They are especially found in the marsupia and near the peristome. 
— - It is highly interesting that it proves to be specifically distinct from the species 
occurring in exactly the same manner on the nearly related Kerguelen-form, Abatus 
cordatus , viz. Lepton parasiticum ÜALL. The deep sea between Kerguelen and South 
America thus forms a boundary for both the host and its parasite (commensaliste). 
On the other hand the Lepton- species found on A. cavernosus is likewise found on 
A. Agassizii , which occurs together with, or in the same regions as A. cavernosus. 
— The other parasitic Bivalve Mollusc, Scioberetia australis , described by BERNARD 
from A. cavernosus was not found on the specimens in hand. 
The specimens of A. cavernosus before me differ so much in the shape of the 
test that, on comparing the extreme forms, one would hardly think it possible that 
they could really belong to the same species. There are, however, so many inter- 
mediate forms that it seems quite impossible to distinguish them with certainty by 
the shape of the test, and no characters being found in the pedicellariæ or other 
appendages of the test by which to distinguish them, they must all be regarded as 
belonging to the same species, affording a very considerable range of variation. 
The height of the test I have found varying from 58 — 72 %, the breadth from 90 — 
96 % of the length. In PI. X are figured some of the different forms. One form 
alone can be regarded as a separate variety, viz. the var. bidens , which is distin- 
guished by its peculiar globiferous pedicellariæ (PI. XIX. Figs. 32, 39). They differ 
very conspicuously from those of the typical form, the valves ending in two long 
teeth, with a short opening or slit below on the inside of the blade. Also the tri- 
dentate pedicellariæ (PI. XIX. Figs. 35, 42) differ somewhat from those of the typical 
form in the blade being more rounded. Though the pedicellariæ thus afford very 
marked distinguishing characters I have been unable to find any such characters in 
the test or the other structures, and it has thus been thought right to separate this 
form only as a variety of cavernosus. 
10 — 100133. Schwedische Südpolar- Expedition igoi — rgoj. 
