ANIMALS. 165 
answered a similar purpose,—a conclusion powerfully supported by an examination 
of Modiola vulgaris, in which the cartilage is internal, and attached to the surface 
of an excavation in the thickness of both hinge-plates. Now it is not difficult to 
comprehend how easily such a fulcrum could become modified into that of Admondia, 
by the inferior margin of each excavated surface becommg more and more projected 
from the hinge-plate. A modification of this kind is imstructively illustrated by the 
cartilage fulcral plates, or spoon-shaped processes, in both valves of Mya truncata. 
It remains to be observed, that the cartilage-plates in Hdmondia vary somewhat in 
direction, according to species. In Ldmondia unioniformis (Isocardia id., Phillips), and 
Eid. Murchisoniana, they are closer to the surface of the umbonal cavities than in 
Lf. sulcata.' 
The wide space between the cartilage-plates of the present genus indicates that 
the cartilage has been of considerable thickness; but it does not appear to have been 
much thicker than that of Modiola, Lutraria, and Mya. 
The anterior portion of the muscular system of Hdmondiais somewhat peculiar. In 
good casts of Ldmondia sulcata there are four muscular impressions in front of the 
umbone; two large ones perpendicularly situated (the uppermost, which is half the 
size of the lowest, is bounded posteriorly by a slightly elevated ridge), and other 
two, which are very small, situated between and at right angles to the former. The 
lowest of the large impressions may be safely referred to the anterior adductor muscle ; 
while the uppermost, together with the two small ones, I am of opinion belonged to 
the visceral or pedal muscles. The large size of the uppermost muscular impression 
is seemingly indicative of the Mollusk having had a large foot, as is the case with 
Unionide and some other families. 
Concluding from what is at present known, the existence of Hdmondia appears to 
have been confined to the close of the primary period; as species are not yet known to 
occur in any other than the Carboniferous and Permian formations. 
EpMonpDIA MuRcHISONIANA, King. Plate XIV, figs. 14, 15, 16, 17. 
Epmonpi1a Murcuisoniana, King. Catalogue, p. 10, 1848. 
— ELONGATA, Howse. Trans. T. N. F. C., vol. i, p. 243, 1848. 
Diagnosis.—Transversely oblong; mequilateral; rather tumid; slightly wrinkled, 
and finely striated parallel to the margins. Half an inch in width, and three cighths in 
length. Valves with a rectilinear hinge-margin, obtusely rounded or somewhat squared 
lateral extremities, anda flatly convex ventral margin. Cartilage-/ulcra half the length 
of the cardinal line; strongly curving within the umbonal cavities; with the free 
margin of their anterior half deeply sinuated. 
1 The character of the cartilage fulera of Hdmondia is strikingly simulated by the posterior adductor 
muscular plates of Teredo navalis ; and very singularly so by those of 7’. dipennata, in which they are 
actually external, being elevated above the dorsal margin of the valves. 
