Distribution of Inttoral Echinoderms of the West Indies. 69 
Besides these 3 southern species, not found elsewhere in the West 
Indies, 7 other species are not yet known from any place but Tobago. 
One of these is the little Thyone, referred to on page 63, but the 
others are all brittle-stars. Of these, two are ophiodermas and deserve 
special attention. One, Ophioderma squamosissimum, has long been 
known from the unique holotype in the Copenhagen Museum, which 
is from an unknown locality in the West Indies, almost certainly not 
Tobago and very possibly St. Thomas. This brilliantly colored 
brittle-star (plate 3, fig. 2) is rare at Tobago, only 5 specimens being 
found on Buccoo Reef at extreme low-tide. None is as large as the 
holotype. The other notable Ophioderma at Tobago is O. phenium 
H. L. Clark (1918, Bull. M. C. Z., 62, p. 333), which seems to be a 
fairly common, endemic species. The coloration is conspicuous, some- 
times all green, sometimes all red, but usually a red disk with green 
arms (plate 3, fig. 1). Another remarkable Ophioderma, O. guttatum, 
is common on Buccoo Reef and reaches a large size there. It is pos- 
sible that this is a southern species, for while it was described from a 
single specimen taken at St. Thomas, and I have taken it twice in 
Jamaica, these three specimens are all small, only about half as large 
as the adults of Tobago. Associated with the ophiodermas on Buccoo 
Reef were great numbers of Ophiomyzxa flaccida, of very diverse hues; 
olive-green either with or without white markings is a usual color for 
this species, but olive-yellow, passing into brilliant yellow (plate 1, 
fig. 2) or brown passing through red-brown into red of various shades 
(plate 1, fig. 1) are common. Another brilliant brittle-star found on 
Buccoo Reef was the unique type-specimen of Ophiothrix erstedii var. 
lutea H. L. Clark (1918, Bull. M. C. Z., 62, p. 314), whose bright 
orange coloration (plate 2) is very distinctive.! 
All of the half-dozen tropicopolitan echinoderms of the West Indies 
are common at Tobago and there are two species which have northern 
rather than southern relationships. One of these is the sea-urchin, 
Arbacia punctulata, whose distribution from Tobago to Massachusetts 
(along the mainland coast?) is so puzzling. Of the remaining 45 species, 
three-fifths are typically West Indian. 
No fewer than 32 species are common to Bermuda and Tobago; 
this is 76 per cent of the Bermudan fauna and is a very remarkable 
fact. It can be explained only on the ground that Tobago is the home 
of 45 tropical Atlantic and West Indian species, and it is from this 
wide-ranging group that the Bermudan littoral echinoderm fauna 
has been almost wholly derived. Of the Jamaican fauna, 43 species 
(69 per cent) occur at Tobago, and of the St. Thomas fauna, 38 (68 
per cent). There are 45 species common to Tobago and the Tortugas, 
but this is only 59 per cent of the Tortugas fauna. 
1I am indebted to Dr. Mayor for making colored sketches from living specimens of these bril- 
liant ophiurans. From these sketches and the preserved specimens, Mr. J. Henry Blake has made 
the beautiful drawings reproduced herewith. 
