ANNOTATED LIST. 151 
have now, any trace of red in the coloration. All but the smallest are unicolor, nearly or 
quite black in life, save for the conspicuously white milled rings on the primary spines. 
In the dry specimens the primary spines are dull olive-green, either light or dark; the 
milled rings are no longer white, but are buff or cream-color. In the specimen from Erub 
the small spines around the peristome are more or less distinctly banded, and in the one 
from Green Island, which is very small (length of test only 6 mm.), even the primaries are 
banded distally. The largest specimen has the test about 32 mm. long, 27 mm. wide, and 
17 mm. high; the primary spines at ambitus are 25 mm. long. This seems to be much the 
largest specimen of Parasalenia as yet recorded. It is further remarkable in that oculars 
I and II are in contact with the periproct, just as in Gymnechinus, a condition hitherto 
unknown in the Echinometride. 
Echinometra mathei. 
Echinus mathei de Blainville. 1825. Dict. Sci. Nat., 37, p. 94. 
Echinometra mathei de Blainville. 1830. Dict. Sci. Nat., 60, p. 206. 
This is probably the commonest sea-urchin in the world, as it ranges throughout the 
full extent of the vast Indo-Pacific region and is more or less gregarious in its habits. Wher- 
ever local conditions permit it is abundant. And yet I have failed to find published a really 
satisfactory figure! 
At both Erub and Mer, mathawi was exceedingly common, and very variable in both 
color and form. Particularly on the southeastern reef-flat at Mer did it abound, and special 
efforts were made there to correlate color or form or both to details of habitat, but all such 
attempts were in vain. 
Heterocentrotus mamillatus. 
Echinus mamillatus Linné. 1758. Sys. Nat., ed. 10, p. 667. 
Heterocentrotus mamillatus Brandt. 1835. Prod. Desc. Anim., p. 266 (66).—H. L. Clark. 1912. Mem. Mus. 
Comp. Zodl., 34, pls. 115-117. 
It is interesting to find this species of Heterocentrotus at Mer, because previous evi- 
dence indicated that it is the more northern form and that if a member of the genus oc- 
curred in Torres Strait, which was hardly to be expected, it would prove to be trigonarius. 
Although only two specimens were found, both are mamillatus, and show no notable 
peculiarities. One was brought to the laboratory by a native boy, and the other was 
found on the eastern reef-flat under a large rock-fragment. 
ARACHNOIDID£E. 
Arachnoides placenta. 
Echinus placenta Linné. 1758. Sys. Nat., ed. 10, p. 666. 
Arachnoides placenta Agassiz. 1841. Mon. Ech.: Mon. Scut., p. 94, pl. 21, figs. 35-42. 
Déderlein (1903) lists this species from Thursday Island, and there are records in 
the ‘Revision of the Echini” from Cape York and Torres Strait. There are specimens in 
the Museum of Comparative Zoélogy from Samoa, New Zealand, Port Mackay, and Port 
Denison, Queensland, Lombok, the Philippines, and Singapore. Bell (1899) lists it from 
New Britain, and Sluiter (1895a) records specimens from Timor and Java. There is no 
other echinoderm with this distribution. 
LAGANID#E. 
Laganum decagonale. 
Scutella decagonalis de Blainville. 1827. Dict. Sci. Nat., 48, p. 229. 
Laganum decagonum Agassiz. 1841. Mon. Ech.: Mon. Scut., p. 112, pl. 23, figs. 16-20. 
Laganum decagonale Bell. 1884. Alert Rep., p. 122. 
Although the three previous expeditions to Torres Strait collected laganids which 
A. Agassiz, Bell, and Déderlein refer to this species, we did not meet with it at any point. 
