Geology and Paleontology. 925 
lips, Eucladocrinus millebranchiatus Wachs. and Sp., Platycrinus 
hemisphericus M. and W., Arthroacantha punctobrachiata Wil- 
liams, Pterotocrinus acutus Weth., P. bifurcatus Weth., P. spatula- 
tus Weth., Cromyocrinus simplex Trauts., Scaphiocrinus sp. und. 
and Actinocrinus verrucosus Hall. It will be observed that in all 
the above species, with two exceptions, the vault is more or less 
depressed or nearly flat, with a simple anal opening, while in the 
last species mentioned the anal aperture is at the extremity of a 
prolonged anal tube—the so-called “ proboscis ”—but in this single 
instance the tube appeared to be injured, and probably has a second 
opening at the base. In every example, whether attached to the 
vault, as in the majority of the genera, or to the side of the calyx, 
as in Platycrinus, the molluscan shell is situated over the anal: 
opening. 
Summing up the predominant physiological and structural 
features suggested by recent investigations, it appears: (1) that the 
Platyceras was attached to the crinoid for a considerable length of 
time, and very probably for life, as is evidenced by the margin of 
the gastropod shell, corresponding exactly to the irregularities of 
the crinoidal surface—first suggested by Meek and Worthen ; (2) 
that the anterior portion of the shell is always directly over the 
anal aperture of the crinoid, and that as growth in the shell con- 
tinues the posterior margin is removed farther and farther from the 
vault opening, as is shown by the shallow concentric channels made 
y the margin of the shell in the vaults of Strotocrinus and Physe- 
tocrinus ; (3) that the nourishment of the mollusc must have been 
derived chiefly from the excrementitious matter from the crinoid, 
though the gasteropod may have subsisted also on animalcules and 
microscopic plants, as in the case of the living representatives of 
the closely allied genus Capulus ; (4) that the shape of the shell 
aperture and its marginal configuration were dependent entirely 
upon the surface of attachment, and hence are of small classificatory 
' value; and 0) that the entire form of the shell was determined to 
a greater or lesser extent by the surface upon which the gasteropod 
was stationed. 
The species of Platyceras in which the sedentary habits are posi- 
tively known from the attachment of the gasteropod shells to crin- 
oids are: P., equilaterum Hall, P. infundibulum M. and W., P. 
parasiticus Trauts., P. erectum Hall, P. formosum Keyes, P. ches- 
terense M. and W., P. dumosum Conrad, and several undetermined 
species.— Charles R. Keyes. 
GLYPTOCEPHALUS NOT IDENTICAL WITH BucKLANDIUM.— 
In the AMERICAN NATURALIST for May and September, 1888 (Vol. 
XXII., pp. 448, 828), I have used the name Bucklandium (Keenig) 
as a substitute for Glyptocephalus of Agassiz (1843), the latter name 
