LAMELLIBRANCHIATA. ] UPPER PALAOZOIC MOLLUSCA. 505 
marked with fine, crowded, unequal wrinkles (averaging four to six in three lines at the middle of the shell), 
which change into broad, obsolete undulations on the posterior slope (three in six lines at two inches from the 
beak) after passing over the obscurely marked, diagonal ridge which runs from the beak to the respiratory 
angle; posterior end broader than the anterior, obliquely subtruncate; slightly gaping at both ends; hinge-line 
with a very slight upward curvature, nearly as long as the shell, the margin inflected to form a broad, concave, 
posterior lunette, or coneaye horizontal cartilage support, with prominent, obtuse, external boundaries. Casts 
shew in each valve a deep furrow from the beak nearly to the posterior end, left by the thick internal ridge 
running close under the dorsal margin: impression of the anterior adductor large, strong, ovate, surmounted by 
the small accessory impression; a nearly vertical, slightly curved ridge from the beak behind them leaves a sulcus 
in the cast; posterior adductor and posterior part of pallial scar superficial, leaving scarcely any trace. Sub- 
stance of the shell excessively thin (about one-fifth of a line); periostraca sharply and irregularly striated con- 
25 
eentrically. Length about six inches, proportional width from beak to ventral margin 3, width of posterior 
end ;4, length of anterior end =, depth of both valves, greatest about the middle, }4, width of posterior 
lunette =. 
This shell resembles an Jridina in form. The substance of the valves is extremely thin, and when well- 
preserved, of a brown horny appearance, minutely plicated parallel with the margin. There is a slight depression 
parallel to and a little below the hing-line; the oblique posterior ridge is much better marked in some 
specimens than in others; above it the undulations of the surface are broad, and slightly convex, but imme- 
diately below it suddenly diminish in size and increase in number, and becoming less prominent, continue so to 
the anterior end; the depth of the shell gradually but slightly increases from the anterior to the posterior 
extremity. This shell is distinguished from the S. wndata (Portk.) by that species having numerous, strong, 
prominent ridges, continued without any visible increase in number or diminution in size across the body of 
the shell; the anterior side is also much narrower and rounded. The difference from the S. ¢ransversa (Portk.) 
is the narrowness of the posterior end in that species, in which also the superficial markings continue as small 
fine plicee and lines over the whole shell, instead of forming strong, broad, undulations on the posterior side 
as in this. The thick internal ridge below the cardinal margin, which leaves a strong sulcus in the cast, is 
thickest at the posterior end, and gradually tapers to a point, and disappears before reaching the beak, so that 
it is in no way homologous with the cartilage ridge of Edmondia. 
Position and Locality —V ery abundant (usually with the valves connected and open) in the dark limestone 
of Lowick, Northumberland. 'The original Irish localities were Roughan, Dungannon, north of Ireland, in a 
precisely similar limestone to that of Lowick, and in the Calp of Ballintrillick. 
Explanation of Figures.—P1. 3. F. fig. 11, right valve, natural size, shewing a patch of the extremely thin 
shell near the middle of the dorsal margin, the remainder of the specimen being an internal cast, shewing the 
thick cardinal ridge close under the hinge-line in the posterior portion, and the large anterior adductor surmounted 
by its accessory impression at the anterior end; from the limestone of Lowick, Northumberland; fig. 11 a, 
back view, to shew the wide, concave, inflected dorsal margins, and the sulcus left by one of the cardinal ridges, 
tapering to a point before reaching the beak, with two small patches of the very thin shell adhering. 
SANGUINOLITES LUNULATUS (Keyserling Sp.) 
Ref. and Syn. = Amphidesma lunulata Keyserling, Petschoraland, t. 10. f. 16.= Allorisma elegans King, 
Perm. Foss, t. 16. f. 3 to 5. 
Desc.—Longitudinally oblong, very gibbous diagonally, most so along an obscurely-angular sigmoid ridge, 
from the beaks to the respiratory angle; beaks broad, tumid, oblique, compressed ; anterior side rather long, 
obtusely pointed, rounded, much narrowed by a very long, oblique, large, elliptical lunette, extending nearly to 
the ventral margin ; ventral margin slightly and irregularly convex, without distinct sinus ; posterior end slightly 
narrowed, obtuse, obliquely subtruncate ; sides gently convex, often with a slight oblique flattening or concavity 
near the middle, crossed by irregular, obtuse, obsolete wrinkles of growth (about four or five in three lines at 
six lines from the beak) ; posterior slope slightly concave, smooth, the concentric wrinkles at the sides stopping 
372 
