78 IOWA STUDIES IN NATURAL HISTORY 
as defined by Agassiz, but the pores are not distinctly arranged 
in ares of four or five pairs and the peristome has minute and 
numerous detached plates. The spines seem to be of two kinds, 
long and short; the former slightly attenuated at the distal end 
and light green throughout, while the latter are slightly clubbed 
at ends; the clubbed parts are white. The two sorts seem to inter- 
grade, however, although most of them appear quite distinct. 
Only one petalostichan form was found, a small specimen close- 
ly resembling Echinoneus semilunaris that we collected at Antigua 
in 1918. 
The Ophiuroidea were abundant in the shallow pools on the 
landward side of the reefs where the water was comparatively 
quiet. But even here each specimen had an anchor to windward 
in the form of an arm or two thrust into the narrow fissures of 
the rock. Thus an entire specimen was hard to procure. Ophi- 
coma was, as usual, by far the most abundant genus, many times 
outnumbering all others combined. The astonishing variation in 
coloration continually surprised us. Some were almost entirely 
black, others black with large white spots in glaring contrast. One 
had all the spines finely ringed with dark brown and white. 
Ophiocoma echinata was by far the most abundant species. O. 
riisei was also found, although Agassiz in his illustrated catalogue 
of the Museum of Comparative Zoology does not report either 
species from the Pacific. Ophiothriz, with its glassy spinulated 
spines, was occasionally seen. It had the pierced jaws, character- 
istic of the genus, according to Agassiz, the prominent radial 
shields, numerous tooth papille, conspicuous tentacles and bluish 
green color of Ophiothriz. The upper and under arm-plates are 
blotched or finely speckled with dark brown or black. The spines 
themselves are not so long, relatively, as in the West Indian forms 
I have seen. O. longipeda and O. demersa are the only species 
reported by Agassiz as occurring from the tropical Pacific, and 
these do not agree in specific characters with our specimens, which 
may belong to several species. 
Another serpent star has a very close, superficial resemblance to 
Ophiura; the upper arm-plates are broken up as in O. cinerea. 
The barred arms, short arm-spines, scaled disk, slit-like genital 
openings just outside the mouth shields, two tentacle-seales and 
numerous papille are characteristic of the genus. But the re- 
semblance is superficial only, so much so that a careful study con- 
vinees one that it cannot be an Ophiura at all, according io 
