THE GENUS COLOBOCENTROTUS. 3 
by the “Albatross” Tropical Pacific Expedition 1899-1900, on the seaface of 
the reef exposed to the full force of the surf. 
A specimen from Chili is figured in the Revision of the Echini (PI. III‘, 
fig. 3). There are also specimens of this species in the Museum collections 
labelled Valparaiso ?, Callao, Chili, and Peru. 
COLOBOCENTROTUS AND PoDoPHoRA. 
The genus Colobocentrotus was established by Brandt in 1835; he also in- 
eluded in it Podophora atrata Agass., for which Agassiz in 1840 established the 
genus Podophora. With the material at my disposal I have come to the con- 
clusion that the original Colobocentrotus of Brandt may be dismembered into 
two genera, — the one (Podophora Agass.) to include P. atrata and P. pedifera 
(Pls. 7; 20); the other (Colobocentrotus Brandt) limited to Colob. Mertensu 
and Colob. Stimpsoni, the former of which was the first species for which 
Brandt originally established the genus (Plates 33; 34; 37; 38; and 35; 36). 
The species of Colobocentrotus (Plates 33, fig. 3 ; 34, fig. 3; 35, fig. 3; 36, 
fiz. 3) are much flatter than those of Podophora. They are at once distin- 
guished by the elongated coronal plates which carry a larger number of 
primary tubercles uniform in size (arranged in two horizontal rows) in 
both the ambulacral and interambulacral zones than in the species of 
Podophora. There are as many as twelve vertical rows of interambulacral 
tubercles immediately above the ambitus in Colob. Stimpsoni in a specimen 
of 65 mm. in diameter; in a specimen of Podophora pedifera of 55 mm. 
there are eight, and in a specimen of Podophora atrata of 45 mm. there are 
only six vertical rows at the ambitus. 
The outline of the test of the species of Colobocentrotus is elliptical or 
circular, while it is pentagonal in Podophora. The general shape of the test 
of the species of Colobocentrotus and Podophora seems to be fairly constant. 
An outline of the ambitus of each of the four species (see figs. a-d p. 5), with 
their measurement and number of pores in the ambulacral plates on the 
abactinal side, is given for comparison. 
Podophora pedifera Agass. 
Length, denuded, 55 mm. 
Width, denuded, 30 mm. 
Height, denuded, 30 mm. 
Pairs of pores in each ambulacral plate 11, 12, near the ambitus on the 
abactinal side. 
