82 R. Rathbun—Echinoid fauna of Brazil. 
as 100. In this experiment and in all those that follow, proper 
corrections were made for the amount of white light reflected 
by the black disc, this having been previously ascertained, in a 
manner which will be described in a future communication. 
In order to test the correctness of the final result, oe lumin- 
the vermilion, was next measured in the same way; it poral 
26 ats 
a0 black card-board, measured. The gray thus obtained had 
a luminosity of 24°54, that of white card-board being 100. 
Nexi, the value of this same gray was calculated from the 
measured luminosities of the two colored discs, and the propor- 
tions of these colors required to produce a pure gray by mix- 
ture on the rotation apparatus; the calculated value was 25°47. 
This agreement proves the correctness of the photometric 
s assumption, that the Sota 
poeta confirmation. 
Corresponding measurements were made with a green, and 
its complementary purpie disc; also with a blue, and its com- 
plementary yellow disc; the results are given below. 
Luminosity. Gray (observed.) Gray (calculated.) 
MOEMINOD; .... = =. —- 23°38 } : ze 
lue-green, -..----- 26°56 ( 24°54 25°47 
Chrome yellow, ----80°3 : 
Cobalt las, ale ee 5°38 t 54°51 53°92 
Ga ere Seen ee 11 
Purple, 14°83 t 24°94 26°56 
Arr. 1X.—The Geological Commission of Brazil. eon to 
the Echinoid fauna of Brazil; by RicHARD RaTuBu 
THouGH the Geological sasig a a has busied itself in 
investigating the marine fauna at almost every point on the 
coas razil where its jnbote ave extended, yet in a group 
like that of the Echinz, the different shore species of which are 
- so readily found and collected by all travelers, it has been able 
to add very little that is new. In its collections, however, are 
three species which do not seem to have been recorded from 
Brazil before. They are: Diadema setosum Gray, Hipponot 
