268 BRITISH PALAOZOIC FOSSILS. | LAMELLIBRANCHIATA. 
extends towards the beak, just in front of the diagonal ridge; surface marked with concentric, fine, unequal 
strie, a few of which, at irregular distances, are much deeper than the rest, from a step-like change of level in 
the surface. Length of average variety one inch, width from beak to ventral margin “, width from anal angle 
io depth of one valve (greatest about the middle of the diagonal ridge) scarcely ;4. 
Hisinger’s figure appears a little longer than usual, apparently from the imperfection of the thin dorsal 
margin, which only shews the full width in fine specimens. Sowerby distinguishes his Modiola antiqua (not 
the species previously so called by Goldfuss) from the AZ. Ni/soni, by being rather shorter and not gaping. The 
gaping in Hisinger’s figure is obviously because the valves are not closed: if the shell really gaped he would not 
have placed it in Modiola. Mr Salter in describing (and well figuring) the species as new, makes no allusion 
to the above description or figures. 
Position and Locality—Common in the olive Ludlow schists above the white grits at Parklane, Llandeilo, 
Caermarthenshire, and in the similar strata at Middleton Park, Caermarthenshire ; Sowerby’s M. antiqua in 
the Bala schists at Gelli Grin, Bala, Merionethshire, slightly narrower and more convex 
Explanation of Figure.—PI. 1. 1. fig. 21. Natural size, left valve, from Parklane, Llandeilo, 
MOoDIOLOPSIS PLATYPHYLLA (Salt. Sp.) 
Ref. and Syn. = Mytilus platyphyllus Salter, Mem. Geol. Sury. Vol. II. pt. 1. t. 20. f. 13 and 14. 
Sp. Oh.—Oblong; length about twice and half the width; sides compressed; anterior lobe very large, 
elliptically rounded, wide, gently convex, defined by a very wide, shallow sinus in the middle of the ventral 
margin, from which a wide, shallow depression extends towards the beak; posterior end slightly widening, 
very obliquely rounded ; anal angle scarcely defined, diagonal ridge gently convex, posterior slope gradually 
compressed ; respiratory angle narrow, elliptically rounded ; beaks very small, inconspicuous ; anterior muscular 
impressions small, close to the beak. Average length two inches; in proportion to length, greatest width 
(at end of hinge-line) ;;,, from beak to opposite ventral margin 4, length of hinge-line apparently =, length of 
anterior lobe ;;,, width of ditto =, greatest depth of one valve ;4, surface nearly smooth, with numerous small 
concentric wrinkles of growth towards the margin. 
The much less convexity of the valves and considerably larger anterior side, as well as more posterior 
ventral sinus, separate this species from the J/. modiolaris of the lower rocks. 
I should imagine the upper part of the anterior lobe in the Survey figures had not been quite cleared from 
the matrix, as it seems narrower than I have seen. 
Position and Locality.—In the yellowish tilestone of Storm Hill, Llandeilo, Caermarthenshire. 
MoDIOLOPSIS POSTLINEATA (M/*Coy). Pl 1. I. fig. 22. 
Ref.—ld. M*Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. p. 58. 
Sp. Ch.—Oblong, twice as long as wide, shell thin, moderately convex ; beaks small, near the anterior end, 
which is obtusely rounded ; no byssal sinus or hollow from the beak ; posterior end obtuse, obliquely rounded ; 
dorsal and ventral margins nearly parallel, straight ; hinge-line two-thirds the length of the shell, with a nearly 
parallel, delicate hinge-plate running beneath it, with erect dorsal margins ; surface with minute, obsolete, 
transverse wrinkles of growth, except on the flattened posterior slope, which is radiated with fine, close, equal 
strie from the beak. Length one inch; proportional width from the beak to the ventral margin ~. 
Some specimens have a rough general resemblance to the NVuculites poststriatus (Emmons), but they are 
distinguished by the parallelism of the dorsal and ventral margins, smaller beaks, greater transverse diameter, 
&e. It also closely resembles the Cypricardites sectifrons of Conrad; but that is figured with radiating lines 
on the sides as well as the posterior slope ; the anterior part of our specimen is unfortunately imperfect. 
Position and Locality.— Bala rock, Alt yr Anker, Meifod, Montgomeryshire. 
Explanation of Figure.—Natural size, of right valve. 
