144 THE ECHINODERMS OF TORRES STRAIT. 
ECHINOIDEA. SEA-URCHINS. 
The echini are, in the Torres Strait region, the least notable of the five classes 
of echinoderms; neither in number of individuals nor of species are they remarkable. 
Nearly all are well-known forms and few call for extended comment. The Chal- 
lenger collection contained 8 species, while Dr. Coppinger of the Alert brought 
home a dozen. Semon took 8, of which 2 were not taken by either of the earlier 
expeditions. We found 14 species at Mer and took 7 others in the vicinity of Thurs- 
day Island. It is remarkable that only 6 of these 21 were taken by the earlier 
collectors, while they took 12 species with which we did not meet. It is rather 
peculiar that they all found Prionocidaris bispinosa, Temnotrema bothryoides, and 
Laganum decagonale in the vicinity of Thursday Island, while we saw none of them 
anywhere in the Torres Strait region. The only echinoid common to all four collec- 
tions is the characteristically Australian spatangoid Breynia. 
There are thus only 33 echini known from the restricted region under consider- 
ation, and it is not likely this number will be greatly increased by further collecting , 
although dredging and the use of tangles may result in some novelties. Not a 
dozen of the species are really common; fully as many are actually rare and unlikely 
to be found. Most of the species are to be found under large coral slabs or rock- 
fragments, or in their crevices, but the clypeastroids occur only on sandy bottoms, 
while the spatangoids may be found in sandy mud. None of the species except 
the Echinometra seem to be gregarious, but both Centrechinus and Echinothrix 
are sometimes found several together around and under the sheltering rock. Echi- 
nometra may occur in scores among rock-fragments where conditions are favorable. 
Both Centrechinus and Echinothrix are unpleasant creatures to touch when alive, 
as the exceedingly long, sharp, and mobile spines are poisonous and inflict a very 
painful wound, for which time seems to be the only alleviant. All of these dis- 
agreeable echini are handsome animals, especially when seen in bright sunlight, 
and Echinothrix calamaris is perhaps the most beautiful of sea-urchins. Another 
notable species is Tripneustes gratilla, in which the contrasts between the purple 
test, orange spines, and black-and-white pedicels are very striking. As Tripneustes 
lives out on the open reef-flat when adult, not seeking the shelter of rocks, it is one 
of the conspicuous animals on such areas. 
CIDARID£E. 
Prionocidaris bispinosa. 
Cidarites bispinosa Lamarck. 1816. Anim. s. Vert., 3, p. 57. 
Phyllacanthus annulifera A. Agassiz. 1872. Rev. Ech., pt. 1, p. 150. 
Leiocidaris bispinosa Déderlein. 1903. Jena. Denkschr., 8, p. 695, pl. viii, figs. 5-11a. 
Prionocidaris bispinosa Déderlein. 1911. Abh. Senckenb. Naturf. Ges., 34, p. 240. 
The nomenclature of this very variable species has been much confused, but at last 
it seems to be agreed that Lamarck’s name bispinosa is really based on the present form. 
One of the few disappointments of my Australian trip was our failure to meet with this 
species. The Challenger, the Alert, and Dr. Semon all took specimens in the Torres Strait 
region, and I confidently expected to get a good series. The geographical range of bis- 
pinosa extends throughout the East Indies from China and the Gulf of Siam to Queensland, 
