LAMELLIBRANCHIATA. | LOWER PALZOZOIC MOLLUSCA. 259 
near the small anterior end; hinge-line long, straight, forming a small anterior, and a large falciform posterior 
wing, with a linear flattened marginal cartilage facet, longitudinally striated ; shell thick, caleareous ; two long, 
slightly diverging, posterior, lateral teeth, beneath the hinge in one valve, and one in the other (in some types 
very numerous and shorter) ; a few short cardinal teeth radiating beneath and in front of the beaks ; dimyarian, 
anterior impression very strong just in front of the beak, posterior impression larger, but faintly marked, super- 
ficial; pallial scar simple; a shallow byssiferous concavity extends obliquely from the anterior part of the 
ventral margin towards the beak. 
The strong impression of the anterior adductor is very visible in casts, and readily distinguishes this Palaeozoic 
genus from Avicula, in which the little anterior accessory muscle is superficial and scarcely to be seen. The 
substance of the shell is generally thicker and more calcareous than in Avicula, as in it the hinge-teeth are 
sometimes absent and more often present, they are also generally more nearly equivalve. 
PTERINEA ? ASPERULA (M‘Coy). PI. 1. I. fig. 5. 
Ref.—Id. M°Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. p. 60. 
Sp. Ch.—Obliquely ovate; body of the shell evenly convex, abruptly defined from the anterior and 
posterior sides; beaks gibbous ; anterior wing rounded, less than half the length of the posterior wing, which is 
flat, acutely pointed, and extending a little beyond the shell, its posterior margin concave ; posterior end of the 
shell broadly rounded ; entire surface radiated with nearly equal, rough (obscurely tuberculated) ridges, 
separated by flat spaces rather greater than their diameter in width, (six ridges in one line at margin) ; those 
ridges are crossed on the body of the shell by fine wrinkles of growth, which on the wing and towards the 
beak become sharp, definite strize, parallel with the margin. Length from beak to posterior end three and half 
lines; width of posterior wing, from angle to side of shell, =; width from beak to margin **. 
Position and Locality—Common in the black Caradoc shale of Builth Bridge, Radnorshire, 
Lxplanation of Figures.—P\, 1. 1. fig. 5. Left valve, natural size ; fig. 5 a, ditto magnified. 
PreRINEA Boypt (Conrad. Sp.) 
Syn.= Avicula Boydi Conrad, Journ. Acad. Nat. Se. Phil. Vol. VIII. t. 12. f. 4. 
Sp. Ch.—Obliquely ovate, depressed, gently convex, most so towards the beak; posterior slope straight, 
defined ; anterior wing small; posterior wing large, broad, flattened, slightly exceeding the margin of the shell 
in length; posterior margin regularly, but slightly, concave; anterior and ventral margin broadly curved to the 
narrow respiratory angle; surface of sides and wing covered with slender, rough, filiform ridges, of irregular 
size, their own thickness apart (about five in two lines near the middle), crossed at small, nearly equal distances 
by sharp, scalloped concentric scaly lines, and large, obscure, irregular waves of growth. Greatest length (from 
beak to respiratory angle, along the straight posterior slope) one inch seven lines; proportional length from 
beak to end of hinge-line {; width of posterior wing =; depth of left valve about ;°. 
This species is somewhat intermediate between the P. lineata and P. reticulata (Gold.), and it is 
possible that Sowerby’s figure of his Avicula lineata (which is not the P. lineata, Gold.) may be an imperfect 
representation of it; this would require, however, that the figure should be less oblique, the posterior wing 
much larger, and the addition of the numerous concentric, scalloped lines, curving upwards between each 
pair of strie. The nearly allied P. jimbriata (M*Coy), Syn. Sil. Foss. Irel. t. 2. f. 7, differs in its stronger 
sculpturing, and having no radiating ridges on the wings. In old specimens every fifth ridge is often larger 
than the others. 
Position and Locality—Upper Ludlow micaceous quartzite of Brigsteer, Kendal, Westmoreland. 
is] 
sa] 
bo 
