80 Ei. Billings on the structure of the Crinoidea, etc. 
either partly: or wholly concealed under the arm. The “point” 
to which Mr, Lyon alludes is seen above, in fig. 11, just below 
the letter b. It is the same as the “ small triangular pyra- 
~ in C. Canadensis. It is evident that , the shell 
dr 
in the genus Pentremites, e concealment ot the 
hydrospires may also be ‘the result of the widening of the 
arm. This is well shown in P. Car DeKoninck, 
(P. Orbignyanus according to Roemer,) P. Schultait De Ver., 
and several other species. In ‘hoes the apices of ss pyra- 
mids remain near the margin, but the hydrospires are nearly 
covered by the wide arms. This is shown in fig. 11, where the 
ends of the fissures of the hydrospires are seen along the aie 
of the angular ridges which extend from the apices of the 
pyramids to the angles between the arms. I do not think that 
such species can be referred to Pentremites, and if I had spe- 
cimens before me instead of figures only, I would most prob- 
ably institute a new genus for ‘their reception, 
Our specimens of C. Canadensis are well preserved and show 
the characters of the arms perfectly. After many careful ex- 
aminations under the microscope, I can state positively that 
in this species the so-called “ pseudambulacral fields” have no’ 
res. The markings that have hitherto been mistaken for 
ambulacral pores in Codaster are not pores, but the small pits 
or sockets which received the bases of the pinnule. The rays 
therefore in this genus are not ‘‘ pseudambulacral fields,” in the 
sense in which that term is used in descriptions of species of 
Pentremites, but simply recumbent arms, identical in struc- © 
ture with those of the cystidean genera Glyptocystites, Callo- 
cystites, Apiocystites, and others. They lie upon the surface 
. the plates which constitute the shell of the animals—not 
m as in —— The large lateral 
pc is both mouth and vent, and the central opening 
heretofore called the mouth is the ambulacral or more prop- 
erly, the ovarian orifice. As, therefore, Codaster has the arms 
of <Apiocistites, the hydrospires of ‘Pleurocystites and the 
confluent mouth and vent common to all Cystideans, I propose 
pare — it from the ee lastoidea and place it in the order 
ystide 
4. On the a Pentremites. 
In Pentremites the hy i 3 is an elongated, internal sack, 
one side of which is attached to the inside of the shell while 
