228 BULLETIN OF THE 
Shell inequilateral, inequivalve, closed; upper or left valve slightly smaller, 
lower or right valve attached to some extraneous object; external layers 
nacreous; inner surface porcellanous; epidermis none or very little; liga- 
ment linear, minute; cartilage inserted in a triangular pit in the cavity of 
the beak; hinge-line short, straight; inner margins radiatingly wrinkled; pallial 
line simple. Mantle completely open, margin papillose without ocelli; gills 
single, one on each side composed of a single row of long filaments, palpi 
none; anal end of intestine produced, free; sexes separate; foot none; anterior 
adductor single, distinct ; posterior adductor double, and leaving a pair of 
closely approximated subequal impressions on the shell; mouth with distinct 
lips ; visceral mass small. 
Dimya Deshayesiana Rovauvtt. 
Dimya Deshayesiana Rouault, |. c., p. 471, pl. xv. figs. 8, 3a, 3b, 1848. Eocene of 
Bos d’Arros, France, equivalent in age to the Paris Basin eocene. 
Stoliczka, l. c., p. 397, 1871. 
Anomia intustriata D’ Archiac, Mém. Soc. Géologique de France, 2me sér., III. p. 441, 
pl. xiii. figs. (9a, 10a 7), 11, 1848.* 
Dimya Deshayesiana Tate, Woodward, Man. Moll., 2d ed., p. 408, 1871. 
Dimya argentea DaLt. 
Plate IV. Figs. 5a, 5b. 
Shell white, micaceous silvery outside, opaque brilliant porcellanous white 
inside ; irregular, laterally compressed, attached by the beak of the right valve 
(to a dead echinus-test, etc.), which is deeper and larger than the other ; ex- 
terior obscurely finely radiately striate ; outline irregularly ovate, broader be- 
hind; hinge-line short, straight, without notch or auricles ; in well-developed 
examples it has a leaf-shaped wrinkled area on each side of a small impressed 
triangular area, below and partly under which is a small, deep, subtriangular 
pit for the brown horny cartilage; ligament hardly perceptible, linear, nearly 
as long as the hinge-line; interior with an impressed area bounded by the 
* It seems very probable that the shells described as Anomia by D’ Archiac were 
all of the same species as that subsequently described by Rouault. Fig. 11 cer- 
tainly represents the same shell, and it looks as if Figs. 9a and 10a represented 
attached valves of Dimya which had been worn through at the point of attach- 
ment of the lower valve, and the resulting accidental perforation taken to be 
normal by D’Archiac. The interior markings are precisely similar, as far as can 
be judged from the figures. In the absence of specimens, however, it is safer to 
preserve the specific name of Rouault, which certainly relates exclusively to the 
species as we now understand it. Rouault’s paper was read in 1847, but seems to 
have been published in 1848, while the volume appeared as a whole in 1849. 
