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. IIP, 

 fig. 3). There are also specimens of this species in the Museum collections 

 labelled Valparaiso ?, Callao, Chili, and Peru. 



COLOBOCENTEOTUS AND PoDOPHORA. 



The genus Colobocentrotus was established by Brandt in 1835 ; he also in- 

 cluded in \i Podophora atrata Agass., for which Agassiz in 1840 established the '^'CJU / 

 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 (Podoj^hora Agass.) to include P. atrata and P.pedifera 

 (Pis. 7; 20); the other (Colobocentrotus Brandt) limited to Coloh. Mertensii 

 and Coloh. Stimj^soni, 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, 

 fig. 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 Coloh. Stimpsoni in a specimen 

 of 65 mm. in diameter ; in a specimen of Podopliora pedifera of 55 mm. 

 there are eight, and in a specimen of Podopliora 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 ^n the 

 abactinal side, is given for comparison. 



Podophora pedifera Agass. 



Length, denuded, 55 mm. 

 Width, denuded, j^mm. ^ V/ 



Height, denuded, 30 mm. 

 Pairs of pores in each ambulacral plate 11, 12, near the ambitus on the 

 abactinal side. 



