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BRITISH PALAXOZOIC FOSSILS. [ LAMELLIBRANCHIATA, 
PTrERINEA DEMISsA* (Conrad Sp.) Pl. 1.1. fig. 7. 
Ref. and Syn.= Avicula demissa Conrad, Journ. Acad. Phil. Vol. VIII. t. 13, f. 3. Id. Hall, Pal, New 
York, t. 80. f. 2a 6. =? Avicula ampliata (Phil.) Mem. Geol. Surv. Vol. II. t. 23. f. 1. 
Sp. Ch.—Subrhomboidal ; moderately oblique; beaks small; left valve sigmoidally gibbous, most convex 
about the middle ; right valve nearly flat; hinge-line extending generally a little beyond the shell; anterior wing 
forming a small, acute, rounded lobe, with the byssiferous sinus only about as far from the extremity as the 
beak is; anterior and ventral margins broadly rounded ; posterior end obtusely rounded; wing broad, compressed, 
the margin slightly concave to form the short acute angle; surface with fine, sharp, regular, concentric strize, 
separated by rather wide, slightly curved spaces (about four in one line near the middle), abruptly closer and 
finer on the posterior wing: casts of the left valve, the strong anterior adductor impressions close under the 
beak ; a flat, narrow, longitudinally striated, ligamental facet along the hinge-line; two long, approximate, 
posterior lateral teeth extending from behind the beak, rather less than half way to the margin, curving from 
the hinge-line at an angle of about 17°; in front of or just under the beak are a few short, strong teeth, directed 
towards the anterior end of the hinge-line. Greatest length, along the hinge-line one inch two lines, greatest 
proportional width at right angles to middle of hinge-line ;;;. 
This variety differs from the P. rectangularis by its long, curved posterior teeth, and small, acute, 
anterior lobe, and less distance of the sinus from the end; the cardinal teeth are larger, and diverge from the 
hinge more than in the type. 
A specimen from the Malverns shews several small holes in the shell, from each of which radiate specimens 
of a small Cliona, or Vioa, burrowing into the substance of the shell, simply dichotomous at an angle varying 
from 45° to 70°; the branches are rounded, two to three lines long, obtuse and slightly dilated at the tip, with 
a diameter of one-third of a line. As this is the oldest known boring sponge, I have named it Vioa prisca, and 
figured it Pl. 1. B. fig. 1. 
Position and Locality.—Common at Middleton Park, Caermarthenshire ; Upper Ludlow of Benson Knot, 
Kendal, Westmoreland; near Pont-ar-y-Ilechan, Llandeilo, Caermarthenshire ; Malverns, Worcestershire. 
PTERINEA HIANS (M“Coy). PI. 1.1. fig. 6. 
Ref—lId. M*Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. p. 60. 
Sp. Ch._—Rotundato-quadrate ; slightly oblique ; moderately gibbous, most so one-third the length from 
the beaks, which are one-third the length of the hinge-line from the anterior end ; anterior side large, defined by 
a deep hollow, extending nearly at right angles with the hinge-line from before the beak to the ventral margin, in 
which it produces a slight sinus; in front of this it is convex, and then nearer the slightly acute cardinal angle 
another smaller, shallow sinus, from the margin towards the beak: posterior wing broad, compressed, not 
abruptly defined from the body of the shell, slightly acute, and scarcely extending beyond the posterior end of 
the body of the shell, which is obtusely rounded; ventral margin nearly horizontal, slightly convex ; surface 
with close, fine, equal, thread-like radiations, interrupted by slightly irregular, concentric imbrications, about 
half a line apart. Length along hinge-line nine lines; proportional width from beak to middle of yentral 
margin 7. 
This differs from the Avicula emaciata (Conrad) by the large, gaping, anterior side, with its double 
sinus ; the same separates it from a small variety of the A. Boydii (Conrad); it is also more square and 
less oblique than either of these species. The large size of the anterior lobe also separates it from the 
Avicula quadrula (Conrad). 
Position and Locality —From the Aymestry limestone of Mortimer’s Cross, Aymestry, Herefordshire. 
Explanation of Figures.—P\. 1. 1. fig. 6. Left valve, natural size; fig. 6 a, ditto magnified. 
* Probably an extreme variety of P. retroflexa, which see. 
