a 
AGASSIZ: PRELIMINARY REPORT ON THE ECHINI. 75 
a comparatively larger number of plates than in the other pacific species. The 
primary radioles are marked for the great development of the milled ring. 
The primary ambulacral tubercles are small and the two vertical rows are sepa- 
rated by a wide band crowded with minute miliaries. Some of the primary 
radioles are curved at the extremity and their great length is very striking. In 
a specimen measuring 12 mm. in diameter, the radioles were slightly over 
60 mm. in length. 
Station No. 3357, off Mariato Point, 782 fathoms. 
G «3360, on way to Cocos Island, 1672 fathoms. 
« “ 3361, on way to Cocos Island, 1471 fathoms. 
& “ 3362, on way to Cocos Island, 1175 fathoms. 
ce “ 3376, South of Malpelo Island, 1132 fathoms. 
66 * 3380, off Malpelo Island, 899 fathoms. 
= «“ 3407, Galapagos Islands, 885 fathoms. 
a “ 3411, Galapagos Islands, 1189 fathoms. 
me “ 3413, Galapagos Islands, 1260 fathoms. 
ARBACIAD 2, PETERS. 
At Station 3382 in 1793 fathoms we dredged a single specimen of a species 
constituting a new genus (Dialithocidaris), and one which we may consider as 
the Pacific representative of Podocidaris of the West Indies. I am inclined to 
consider as also belonging to this genus Podocidaris prionigera A. Ag., which 
when described was referred with considerable doubt to the genus Podocidaris. 
DIALITHOCIDARIS, A. Ac. 
The genus is marked by the great size of the genital and ocular plates of the 
apical system ; by the width of the interambulacral area, by the peculiar 
linear arrangement of the large interambulacral miliaries along the median line 
parallel with the horizontal sutures of the upper interambulacral plates. The 
plates nearer the ambitus and on the actinal surface each carry two primary 
tubercles. The ambulacral plates carry one primary tubercle. The sutures of 
the abactinal coronal plates are somewhat sunken and bare, as in some species 
of Goniocidaris. 
Dialithocidaris gemmifera A. Ac. 
Plate V. Figs. 1, 2. 
There are only four anal plates in the single specimen we dredged. The 
genital and ocular plates are crowded with irregularly arranged sessile spines, 
either globular or clubshaped. The madreporite is well developed. The ac- 
tinal system is marked by ten large elliptical plates placed in the extension of 
the ambulacral system. The longest primary radioles are 8 mm. in length, 
