260 
Mr. R. Etheridge, Jun., on a 
berg* ; and this shows no dorsal carina ; but (if we interpret 
it aright) it has a peculiar short oblique ridge on each valve, 
intermediate to the vertical anterior and the longer oblique 
hinder ridge, starting with them from the umbo, but reaching 
across only about a third of the valve’s width.” 
Let us now pass on to the fossil more recently discovered by 
Mr. Bennie, and compare it with L. Leidyi and L. tricarinata. 
The Granton species possesses to a great extent the quadrate 
form assumed by the others; but the angles and ventral edge 
are somewhat more rounded than in the type species and its 
variety Williamsoniana , and its angles are blunter than those 
of L. tricarinata. The surface is concentrically ridged, and 
the hinge-line straight, as in the others. The interesting 
feature, however, in connexion with this species, lies in the 
single ridge which crosses each valve in place of the two of 
L. Leidyi , the two and a half of L. Klieveriana , and the three 
of L. tricarinata. Instead of one from the umbo to the 
antero-ventral angle, and another forming a diagonal, as in 
the first—or a similar arrangement with the addition of a 
small, short, intermediate ridge, as in the second—or of a dorsal 
carina, as in the last,—the Granton specimens have only one 
cross ridge, that from the umbo to the antero-ventral angle, 
the diagonal and the dorsal ridges being, so far as we at 
present know, quite absent. 
In the specimens before me this character is constant; and 
if, in the imperfect state of our knowledge of the species of 
this genus, the number of ridges on the carapace is to be taken 
as one of the chief points upon which to base separation, I 
think there can be no impropriety in assigning a special name 
to these individuals with a single ridge. Indeed Prof. Rupert 
Jones at first suggested to me the possibility of this being the 
type of a distinct u genusbut he is now inclined to think 
that the cross ridges had better be regarded (provisionally at 
least) as specific characters, as we know nothing of the 
animal itself, and as there is but little in the shape of the 
valves that can be relied on as a constant character. Under 
these circumstances I shall content myself with describing the 
Granton specimens as Leaia Jonesii , as a slight recognition of 
the kindness and assistance I have always received at the 
hands of Prof. T. Rupert Jones, F.R.S. &c. 
Leaia Jonesii , sp. nov. (Figs. 1, 2.) 
Sp. char. Valves of the carapace oblong, very slightly and 
obliquely acuminate anteriorly, subtruncate and rounded 
* Die fossilen Thiere aus der Steinkohlenformation von Saarbriickeu, 
1877, Heft 2, p. 46. 
