Holothuroidea from Southern Chile — -PAWSON 
radials each have an anterior notch for insertion 
of retractor muscles ( Fig. 2,1). There is a single 
tubular Polian vesicle about 40 mm in length, 
which arises from the water-vascular ring in the 
left dorsal interradius; the madreporite is a very 
small nodule about 1.5 mm in diameter, lying 
near the posterior edge of the calcareous ring in 
the middorsal interradius. The gonad comprises 
two bunches of elongate unbranched orange- 
coloured caeca, which attach to the long genital 
duct near the middle of the body in the mid- 
dorsal interradius. 
The skin is packed with great numbers of cal- 
careous deposits, which chiefly take the form of 
thick, oval plates, with few perforations or none, 
and a length varying between 0.07 mm and 0.2 
mm (Fig. 1, 2) . Overlying the plates are a small 
number of rudimentary "cups” which vary con- 
siderably in shape (Fig. 2, 5), and occasionally 
carry short, blunt knobs, and may have up to 
three perforations. At the extreme posterior end 
of the body the plates are larger, and more com- 
plex, with a great number of perforations, and 
a tendency to become knobbed or two-layered 
(Fig. 2, 4). These plates are up to 0.3 mm long. 
The tube feet contain stout end plates which are 
surrounded by perforated supporting deposits 
(Fig. 2, 3), having an average length of about 
0.2 mm. 
Lampert (1893) apparently stated that this 
species has a calcareous ring with posterior pro- 
longations, as Theel (1886^), after examining 
the "Challenger” specimens of Thy one lechleri, 
stated that "each piece (of the calcareous ring) 
. . . has a bifurcate projection posteriorly.” Then 
Theel ( 188 6b) described a new species, Thy one 
hassleri, which resembled Lampert’s Thyone 
lechleri in most respects, but lacks posterior 
processes on the calcareous ring. Ludwig (1898^) 
illustrated the calcareous ring of what he be- 
lieved to be Thyone lechleri, and it is similar in 
every way to the ring illustrated in this paper 
(Fig. 2, 1), and lacks forked posterior processes. 
Panning (1949) also states that the calcareous 
ring in species lechleri lacks posterior processes. 
Either Theel (1886£) was quite correct in erect- 
ing the species hassleri for those specimens with 
no posterior processes on the calcareous ring (in 
which case some specimens previous workers 
461 
have assigned to species lechleri are in fact has- 
sleri) i, or Lampert’s type specimen of lechleri 
may have been unusual in possessing posterior 
processes. The calcareous deposits of species 
lechleri and hassleri are apparently identical and 
are so unique in character that it seems logical 
to leave the two species as synonyms. The prob- 
lem cannot finally be resolved until Lampert’s 
type material can be re-examined. 
DISTRIBUTION: Tr achy thy one lechleri is 
known from the vicinity of Magellan Straits and 
Tierra del Fuego in depths up to 30 m. A single 
holothurian from Heard Is., resting in the col- 
lection of the Dominion Museum, Wellington, 
was identified by the author as Tr achy thy one 
lechleri, and thus the range of this species is now 
considerably extended. 
Family PSOLIDAE 
Genus Neopsolidium n. gen. 
DIAGNOSIS: Small forms, with sole not sharply 
distinguished from the rest of the body. Dorsal 
deposits small (up to 0.4 mm) smooth per- 
forated plates, and cups. Ventral deposits plates 
similar to dorsal plates and perforated buttons; 
no cups ventrally. 
TYPE SPECIES: Psolidium convergens (He- 
rouard ) . 
REMARKS: Deichmann (1941, 1947) stated 
that the species Psolidium convergens deserves 
a separate genus because of the nature of its dor- 
sal deposits, which differ from those in most 
other Psolidium species. This opinion was based 
chiefly on the thorough description and figures 
given by Perrier ( 1905 ) of this species. Clark 
(1946) agreed with Deichmann, but neither of 
these workers elected to propose a new generic 
name. Examination of specimens of Psolidium 
convergens in the Royal Society collection 
has convinced me that this species should be 
assigned to a separate genus. Although Neop- 
solidium is monotypic at present, it may accom- 
modate some other Psolidium species, and future 
work will show whether or not this is possible. 
The family Psolidae contains but a small num- 
ber of genera, and the genus Psolus itself is in 
urgent need of revision. Such a revision is be- 
yond the scope of this work. 
