E. Billings on the structure of Crinoidea, Cystidea, etc. 225 
Art. XXIII.—WNotes on the structure of the Crinoidea, Cystidea 
and Blastoidea ; by E. Bruurnes, F.G.8., Paleontologist of the 
Geological Survey of Canada. 
(Concluded from this Journal, IT, vol. xlix, p. 58). 
6. On some points relating to the Structure of Pentremites. 
as 
YYYOG 
ee, 
6 
1.—Calycine plates of Pentremites,—b, the basals; f, one of the five forked 
aun B deltoid LEW i, ere plate ; os, oral spiracle; s, spiracle. 
i Sigg — Caryocy testudinarius, Hisinger,—, basal plates; 7, radials; m, 
mouth. 
of growth. The radial system consists of the joints of the stem, 
the centrodorsal plate, the radial plates, the joints of the arms, 
and also those of the pinnules. In the perisomatic system he 
includes the basal and oral plates, the anit plate, the interradial 
pe and any other plates or spicula which may be developed 
n the perisom of the cup or disc. This I thinka good ae 
one except in so far as it regards the stem, which appears to 
me to be, ive a appendage of the perisomatic, rather than 
of the radial syste 
Throughout ua whole range of the Crinoidea, the plates of 
the radial and perisomatic systems, are easily distinguished from 
each other. In general, the Cystidea have no radial plates in 
ee calyces except, perhaps, in a small area around the ambu- 
lacral orifice. This acco well with an — observation 
* On en nutty © cud Antedon rosaceus Linck (Coma rosacea of 
La- 
marck). y Professor WYVILLE THOMPSO: oe Pi &e, Plmebicn Transac- 
ions of es Tnopal Society, Wee elv, Part TL | p. 54 
