Fewkes.] 
116 
[Dec. 5, 
which have a pluteus, or at least the hooked spines do not exist on 
the well-known viviparous Amphiura. 
It is a remarkable fact that the hooked spines, although not con- 
fined to the end of the arm, occupy a prominent position on the 
terminal segment of the arm. In some of the figures with which I 
am familiar, they are represented on the other segments, but they 
are not found elsewhere on the body of the ophiuran. I am also 
unaware that they have been detected in genera which have a di- 
rect development. 
That these spines are not the same functionally as those with 
straight shafts ordinarily found in ophiurans seems to me not to 
admit of doubt, but it seems doubtful whether they are morpho- 
logically the same. I believe that in the genera mentioned they 
are embryonic structures. Are there any adult genera which retain 
these or similar embryonic hooked spines? We naturally turn in 
answering this question to the ophiurans from deep water, which 
from their habitat would seem to preserve embryonic features. Ly- 
man describes from the rich collections made by the “Blake” a most 
interesting ophiuran which has similar hooked spines in specimens 
which may well be considered adult. The genus Ophiobrachion is 
remarkable in several particulars, but in none more so than in the 
possession, on the arms, of rows of uncinate spines. I have seen no 
homology of these spines with those of other genera suggested, 
and suppose that they are believed to be the same as ordinary 
ophiuroid spines, simply with hooks at the end. It seems to me, 
however, that they may be put in the same category as the terminal 
embryonic spines of the young Opliiothrix. In Ophiobrachion they 
are permanent in the adult. 1 
In Astrophyton, also, we have at the tips of the ray divisions of 
the adult spines which are directly comparable with the embryonic 
hooked spines of Opliiothrix. The resemblance of these spines to 
those of the adult Ophiobrachion is commented upon by Lyman in 
his description of the genus. 
It seems therefore necessary to distinguish among the spines of 
ophiurans, as among starfishes, two different kinds of calcifica- 
tions : 
1. The ordinary spines of the adambulacral arm plates. 
1 Similar hooked spines occur in the adult Ophiothrix and in Ophiopteron, according 
to Ludwig. The latter has three different kinds of hyaline spines : 1, hooks; 2, rod-like 
spines; 3, supporting rods of the membranous fins. 
