210 
PACIFIC SCIENCE, Vol. XX, April 1966 
The remainder of the area is sculptured, so that 
in this aboral region the median sutures of the 
ambulacral plates cannot be seen. Slightly larger 
specimens show faint traces of an epistroma, 
but these soon disappear as the animal grows. 
This parallels the situation in P. novaezea- 
landiae and P. albocinctus, where the epistroma 
disappears before maturity is reached ( Fell, 
1958:36). 
The stomach contents of several specimens 
consisted almost entirely of fragments of a 
brown alga, probably Macrocystis. This spe- 
cies appears to be predominantly a vegetarian 
browser. 
DISTRIBUTION : P. magellanicus is well known 
from the southern part of South America. To 
the east the northern limit of its range is about 
35°S (Rio de la Plata), and to the west the 
northern limit is about 41 °S (Puerto Montt). 
The species also occurs at Tristan da Cunha. It 
is extremely common in some areas, and appears 
to favour life in the Macrocystis zone, where it 
may be found in large numbers on the fronds 
of Macrocystis. 
Family strongylocentrotidae Gregory, 
1900 
Loxechinus Desor, 1856 
TYPE SPECIES: Loxechinus alhus (Molina). 
REMARKS: This genus is monotypic. 
Loxechinus albus (Molina) 
Loxechinus albus Mortensen, 1943: 172 (com- 
plete list of references), pi LVII, figs. 18-19; 
1952: 10; Bernasconi, 1953:23, pi. VII, fig. 1, pi. 
XI, pi XII, figs. 1-9. 
MATERIAL EXAMINED: 16 specimens, from 
Stn. 39 (5); Stn. 51 (2); Stn. 57 (1); Stn. 
70 (8). 
REMARKS: The largest specimen has a hori- 
zontal diameter of 82 mm and a height of 40 
mm, and the smallest 23 mm and 13 mm, re- 
spectively. In all specimens the radicles are 
green, and the denuded test is faintly purple 
admedially in the ambulacra and interambu- 
lacra, green elsewhere. 
distribution: This species is known to oc- 
cur on the west coast of southern South Amer- 
ica, as far north as Callao, Peru. While its depth 
range is 0-340 m, it is most commonly found 
in the littoral zone, where it may be extremely 
abundant. 
DISCUSSION 
In area 1 (Isla Chiloe, Stns. 1-19), no echi- 
noids were collected, although Professor Knox 
(personal communication) noted the presence 
of a common sea urchin (probably L. albus ) on 
the rocky coasts. 
The three species in the collection were taken 
from the other two areas, Puerto Eden to Punta 
Arenas (Stns. 19-49) and Isla Navarino (Stns. 
50-78), where they are all represented in the 
rocky infralittoral zone. 
Species not represented in the collection, but 
known to occur in southern Chile, include the 
arbaciid Tetrapygus niger (Molina) and the 
schizasterids Tripylus excavatus Philippi and 
Tripylaster philippi (Gray). 
The known echinoid fauna of this region is 
related to the faunas of other subantarctic or 
cold temperate localities at the generic level. 
Pseudechinus is a southern genus, with species 
on many subantarctic islands. Arbacia appears 
to have the west coast of South America as its 
centre of distribution, whence species have 
spread to the east coast, and to the Atlantic 
coast of Africa (Mortensen, 1935). The genera 
Loxechinus and Tetrapygus are monotypic, and 
their species are known only from the south- 
western coast of South America. Tripylus has 
three species in the Antarctic seas, and a single 
species is known from the southern tip of South 
America. Tropical genera are not conspicuous 
in the shallow water fauna. 
REFERENCES 
Bernasconi, I. 1953. Monografia de los equi- 
nodermos Argentinos. Ann. Mus. Hist. Nat. 
Montevideo 2 (6): 1-58, pis. I-XXXII. 
Fell, H. Barraclough. 1958. Deep-sea echi- 
noderms of New Zealand. Zool. Publ. Vic- 
toria Univ. Wellington 24:1-40, pis. 1-5. 
— 1962. Embry ological evidence of evolu- 
tionary trends in some temnopleurid echi- 
noids. In: G. W. Leeper, The Evolution of 
