1907-8. ] NOTES ON THE OPHIURIAN GENUS, PROTASTER 371 
outer ends of these plates, the ten others converge in pairs to the centre 
of each ray ; these may be analogous to the forked wings of the proximal 
ambulacral plates. Figure 5 shows the three first ossicles of one side’ 
with the wings worn away, and exhibits the manner in which the outer 
rosette plates abut against the first ambulacral ossicle. 
Little is known of the oral apparatus. The syngnaths are formed 
from the adambulacral plates. They consist of stout curved rods 
projecting inwards and curving upwards at their inner ends. (Fig. 4.) 
The present species differs from the genotype, as figured by Gregory, 
in that the ambulacral ossicles are not crossed by a transverse groove on 
their ventral surface,and by the shorter length of the “toe” of the 
“boot.” The ossicles are very like those of Protaster biforis, Gregory, 
but the adambulacral ossicles and side plates are very different ; in this 
latter respect the form approaches Bundenbachia, Stiirtz. The arrange- 
ment and shape of both sets of ossicles are much like those of 
Lapworthura miltont, Salter, sp., except for the fact that in this species 
the ossicles are opposite and not alternate. From P. forbesz, Hall, it 
differs in the greater size, the strict alternation of the ossicles and the 
absence of spines. The most striking similarity was observed with 
respect to T@nzaster elegans, S. A. Miller. While this form is only half 
the size of the present species and from a much higher formation ‘the 
top of the Hudson River), there is nevertheless a close resemblance in 
the shape and arrangement of the ossicles. 7. elegans is, however, 
spinous, and lacks a disc, according to its author, who had over thirty 
specimens to examine. It is doubtful if the original absence of a disc 
can be confirmed in a species so strikingly like the one under 
review. 
Dr. Whiteaves has kindly allowed me to examine the types of 
Tentaster cylindricus, Billings. In one only of these specimens can the 
shape and arrangement of the ambulacral ossicles be seen, and then only 
very indistinctly. They appear to have an inferior aspect, approximating 
to boot-shaped, and they are almost uniformly opposite. I shou!d be 
inclined to place this specimen under Lapworthura of Gregory. In 
establishing the genus 7@nzura for the reception of Tenzaster cylindricus, 
Dr. Gregory states that the ambulacral ossicles are “rods lying parallel 
to the arms.” It is apparent, therefore, that he based his description on 
different specimens from the one now in my hands. In any event, the 
new species is distinct, for it is more than twice as large, the ossicles 
