326 CRETACEOUS GASTROPODA 
The only objections which could be raised against the classification of the genus 
in this family would lie in the supposed small opening of the apex, which, if present, 
would refer Anisomyon to the Fissurertips. The existence of a perforated apex 
is, however, by no means settled, and from its length it would appear more 
likely that its point was broken away. On the other hand its thin shell very 
much recalls similar forms of Umbrelle and other PLEUROBRANCHIATA. Gabb 
quotes in his Synopsis of American fossils (Am. Phil. Jour. 1861, VIII, p. 94), 
the following six species, Anisomyon alveolatus, M. and H.; A. Shwnardi, 
M. and H.; 4. borealis, Mort.; A. patelliformis, M. and H.; A. sexsuleatus, 
M. and H., and A. subovatus, M. and H., (for other references see Proc. Acad. Nat. 
Sc. for 1860, p. 423). To these is to be added A. Meekii, Gabb (Pal. Calif. I, 
1864, p. 142, pl. 21, fig. 105). Meek, (Check list, cret. foss., 1864, p. 17) has 
an A. Haydent and a doubtful A. ? imequicostatus (Scalpellum id. Shumard). 
The same author quotes an A. alveatus, M. and H., which is probably a misprint 
for A. alveolatus. 
The genus Anisomyon is classed by Meek in the family TYecrurinz; at 
present only American species have been recorded under this name, but there 
is a large number of fossils known from the cretaceous beds of Europe, des- 
eribed under Helcion, Acmea, (Tectura) and Patella, which when found in better 
preservation and after having been more carefully examined, will largely increase 
the number of species belonging to this genus. 
XLVII. Family,—STIPHONARITID AL. 
H. and A. Adams, Genera, II, p. 268; Deshayes, Anim. s. vert. foss. Paris, iI, p. 687, ete. 
The distinctions between the animals and shells of Gadinia and Siphonaria 
do not seem to be so very great as to indicate the separation, which has 
been proposed for the two respective families by the authors of the “ Genera.” 
H. and A. Adams transfer, namely, Siphonaria to the neighbourhood of Ancylus 
and Amphibola. 'The tentacles of Siphonaria are thickened and expanded, forming 
a sort of fleshy disk, and having the eyes sessile near their base, or at their outer 
margin. Their expansion is generally not stronger, or scarcely stronger, than in 
Gadinia, only that they are less distinctly separated than in the last genus. The 
branchial plume —if it really deserves that name -—is single, running across the back, 
but the respiratory opening which is placed anteriorly on the right side, is covered 
by a fleshy lobe of the mantle, and the presence of this lobe is, strictly speaking, the 
only remarkable difference between the two families. The foot forms a tolerably 
expanded, oval, fleshy disk. The teeth are numerous, sub-equal, arranged in 
slightly curved cross-lines: the central tooth being narrow, elongated, with a small 
rhombic apex; the lateral teeth larger, diverging and furnished with curved tips. 
The teeth of Gadinia are as yet not. known and cannot, therefore, be brought 
in support of the relations of the two families. The shells of Stphonaria, the only 
genus known as constituting the family, are depressedly conical and usually 
