SALENIA VARISPIXA. 15 
stages collected the pairs of buccal plates are quite distant. In the abactinal 
system the differences due to age are quite marked. The plates covering 
the anal opening are few in number, and comparatively large in the j'ounger 
stao-es; with increasing size the ])lates become more numerous and relatively 
smaller, and carry from one to two minute tubercles. The granulation of 
the genital and ocular plates becomes also more distinct with increasing size, 
forming more or less regularly radiating lines ; the outer edges of the plates 
of the genital ring become also somewhat indented, the inner edges of the 
ocular plates are grooved in the extension of the radiating lines of the gran- 
ules of these plates. The gills of *S'. PaUersord are stouter and less branching 
than the gills of *S'. varispina, and the few sphseridia noticed are remarkable 
for their small size and globular outline ; one or two sphanidia are placed in 
the ambulacral areas close to the edge of the ocular plates, 
Salenia varispina A. Ac. 
This species, of which only a single young specimen had been collected by Mi\ Poiirtales, has been 
found from Lat. 24° 36' N., Long. 84° 5' W., as far as Granada and Barbados, in depths of 
334-1,20(1 fathoms. It is naost abundant in depths between 400 and GOO fathoms. 
For otlier localities, see Bull. M. C. Z., V., No. !), p. 186, ]878 ; VIII., No. 2, p. 71, 1880. 
PL VI. Fir/s. 1-17. 
How fiir the obliquity of the axis of tlie apical system is a structural feature 
of sufficient importance to be considered a generic diflerence, it is difficult to 
decide. In Salenia we undoubtedl}' have in the asymmetrical arrangement 
of the plates of the apical system a feature somewhat prominently developed, 
which is found in all Echinoderms, and which is due to the original mode of 
growth of the plates of the embryo Echinoderm in a spiral curve. Traces of 
this are plainly to be seen in the unequal development of the genital and 
ocular plates throughout the group of Echini, in no one of wliich do v/e find 
the five plates either of the genital or ocular system symmetrically devel- 
oped, or exactly symmetrically arranged in relation to a longitudinal axis. 
We find this in the apical system of the Patechinidte, the Echinothurias, the 
Cidaridaj, the Echinida?, the Clypeastroids, and tlie Spatangoids, as well as 
in the asymmetrical test of all young Echinoidea ; and perhaps we may trace 
the different degree of development of the five seines of ambulacral and inter- 
ambulacral zones throughout the group of Echini to such a primitive differen- 
tiation. As Neumayr has suggested, the appearance of the suranal plate in 
Salenia may not have the meaning or importance which has been attached to 
v^g/ 
VOO 
