Mr. F. J. Bell on the Genus Crossaster. 141 
all the facts which can be made out with regard to these two 
forms, which he retains in one genus. 
I will here only direct attention to the gradation in cha- 
racters, which, till the publication of Messrs. Danielssen and 
Koren’s studies, induces me to regard Solaster, Crossaster, 
and Lophaster as distinct genera. 
When we examine the actinal surface of a ray of S. endeca 
we observe that, externally to the transverse set of spines 
which runs near the ambulacral groove, there is a series of 
special plates bearing a comb of spines: though in a sense 
marginal, these plates are quite confined to the actinal sur- 
face; from the dorsal view one would not have the least 
suspicion of their existence. It is not so with C. papposus ; 
for in it the modified marginal plates are set on the upper 
part of the side of the ray, and form a regular series of dorso- 
marginal plates. Coming lastly to Lophaster, we find that 
the “differentiated marginal plates” of which Prof. Verrill 
speaks exhibit a striking advance on what has been seen in 
Solaster or in Orossaster: there are now two sets, one dorso- 
marginal and one ventro-marginal. 
A gradational series so well marked does, I submit, afford 
very considerable support to the view that the three forms in 
question belong to distinct though allied genera. 
Crossaster neptunt, 1. sp. 
Arms ten: R=50, r=25. 
A species of the character of C. papposus, but distinguished 
from it by the absence of the glassy spines on the paxille 
and by the smaller number, larger size, and greater regularity 
of the paxille themselves. 
The spines in the single adambulacral row which fringes 
the groove are generally placed by threes on each plate; near 
the actinostome, however, four spines may be found on a 
plate; the spines are short and stout. About five or six 
similarly rather stout spines are found in each set of the trans- 
verse rows; they are not spread out in fan-shape, as they are 
in S. papposus. ‘The interbrachial space is small, and has 
scattered over it pairs or triplets of short spines, just suffi- 
ciently numerous to relieve it from an appearance of bareness. 
The outer free edge of this space (interbrachial angle) 1s 
occupied by a collection of small spines arranged in form of a 
double tooth-comb; there are about twelve of these special 
bundles of spines; and they, as they pass outwards, rapidly 
mount to the dorsal edge of the arm, to which they give a 
very characteristic appearance. The double tooth-comb 
arrangement soon yields to a more irregular disposition, and 
