PALEOPNEUSTES CEISTATUS. 59 
at the extremity of the petaloid ambulacra or the petals themselves, as in 
one of the species of Ehinobrissus, but crossing them below the petals at 
an indefinite place of the test ; so that we might have an interior fasciole, as 
in Lovenia ; a true peripetalous fasciole, as in Hemiaster ; a transpetaloid 
fasciole, as in Gualteria and Ehinobrissus ; or a marginal fasciole, as in some 
stages of growth of Paleopneustes and in Linopneustes ; all representing 
different stages of development or modification of a petaloid fasciole. This 
simple series becomes complicated with the possible sunultaueous existence 
of an internal and peripetalous fasciole or of a true peripetalous fasciole 
with a more or less marginal fasciole, forming in that case a lateral fasciole 
proper. In a specimen of tliis species measuring about 85 mm. in length, 
the marginal fasciole is traced only with difficulty near the ambitus across 
the anterior lateral ambulacra (PI. XXI. Fig. 8), and it seems to disappear 
completely in somewhat older specimens. But in all the stages of growth 
that part of the ambitus and' of the test adjoining the course of the mar- 
ginal fasciole is thickly studded with miliaries and small secondary tubercles 
(PI. XXI. Figs. 2, 6, 8). 
In Linopneustes this marginal fasciole has assumed practically all the 
characters of a peripetalous fasciole crossing the posterior lateral ambulacra 
just at the end of the petals, while it still crosses the anterior ambulacra a 
short distance below the end of the petals. Neither in Paleopneustes cristatus 
nor in P. hjsfrix do we find any trace of a rudimentary subanal fasciole, either 
as an indistinct band or a part of a band, or even as accumulations of miliary 
tubercles ; and it is interesting to note that in species so closelj' allied as 
P. cristatus and Linopneustes Miirrayi there should be so striking a distin- 
guishing feature as the presence or absence of a subanal fasciole, while 
in other genera of Spatangoids, Palajotropus, Urechinus, and Schizaster, in 
specimens of the same species, such as Urechinus naresianus, we should have a 
complete series passing from a well-defined subanal fasciole to a mere accu- 
mulation of miliary tubercles. 
The smallest specimen collected, measuring about 16 mm. in length, is 
somewhat more flattened than the older stages, and shows as yet no trace of 
petals, the ambulacral plates and pores extending uniformly from the apex 
to the ambitus and actinostome without the specialization of any portion. 
(PI. XXI. Figs. 9-11.) In this stage I could see no indication of a marginal 
fasciole. The apex was compact, but there was no trace as yet of any 
genital openings, and the madreporic body was very faintly indicated (PI. 
