264 BRITISH PALAXOZOIC FOSSILS. [ LAMELLIBRANCHIATA. 
tooth or hinge-plate as long as the hinge-line, and close beneath it; a thick internal ridge (often leaving a sulcus 
in casts) curves from behind the beak towards the yentral margin at an angle of about 50° to 60° from the 
hinge-line ; hinge-line crenulated, forming arca-like transverse teeth in front of the beak. Length four and 
half lines, width from beak to opposite ventral margin =. 
This little species is much less elongate, and has a more obtuse posterior wing than the A vicula insueta 
(Conrad), which it otherwise much resembles. The abrupt bending down of the curved internal ridge, like a 
lateral tooth into the body of the shell, is a curious character in which, as well as general form, it agrees with 
the P. sublavis (M°Coy) of the Irish silurian rocks, but from which it is distinguished by its fine close striation. 
Position and Locality —Common in the Upper Ludlow shale of Cwm Craig Ddu, Builth, Brecknock- 
shire; Middleton Park, Caermarthenshire; Erw Gilfach, Builth; and in the Ludlow schists above Parklane, 
Llandeilo, Caermarthenshire; Upper Ludlow of Benson Knot, Kendal, Westmoreland; also in the sandy 
schists of Pont-ar-y-llechan, Llandeilo, Caermarthenshire ; in the olive flags above Ravenstone Dale, West- 
moreland ; Upper Ludlow, Burton and Brockton ; Upper Ludlow near Ludlow, Shropshire. 
Explanation of Figures.—P\. 1.1. fig. 4. Natural size, left valve, from Benson Knot; fig. 4a, ditto, 
magnified. 
Genus. AMBONYCHIA (fail). 
Gen. Char.—Inequivalve*, inequilateral, obliquely ovate or suborbicular, inflated ; beaks small, prominent, 
incurved ; anterior side very short, rounded ; ventral margin broadly rounded; posterior side broad, compressed, 
subalate ; hinge-line less than the width of the shell, oblique, anal cardinal angle obtuse ; surface either longi- 
tudinally suleated, or with broad concentric wrinkles; one large subcentral muscular impression in each yalve. 
Often confounded with Jnoceramus, from which it differs by wanting the transverse pits in the hinge; and 
with Prerinea and Avicula, from which it differs in its short hinge-line and having no anterior wing. Cardiola 
has not the angular posterior wing, and has an area between the beaks. 
AMBONYCHIA ? AcuticosraTA (J/’Coy). Pl. 1. K. fig. 16. 
Ref—Ild. M°Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. p. 59. 
Sp. Ch.—Ovyate, moderately and evenly convex, most so towards the beak ; surface radiated with numerous 
angular ridges, only separated by the angular sulcus formed by the meeting of the steep sides of the ridges 
(about six ridges in one-fourth of an inch of the margin at half an inch from the beak). 
In form and number of the ridges this resembles the small specimen of A. carinata (Gold. sp.) figured in 
Hall’s Paleontology (PI. 80. f. 5), but it is distinguished by its ribs being angular and close together—they 
being rounded and separated by flat interspaces in the American form. 
Only one imperfect specimen has occurred, measuring seven lines from beak to ventral margin. 
Position and Locality.—In the green schists of Dinas Bran, Llangollen, Denbighshire. 
Explanation of Figures.—P\, 1. K. fig. 16. Natural size ; fig. 16 a, superficial ridges of ditto magnified. 
AMBONYCHIA STRIATA (Sow. Sp.) 
Ref. and Syn. = Cardium striatum Sow, Sil. Syst. t. 6. f. 2. 
Sp. Ch.—Obliquely ovate, slightly convex, beaks very prominent, obtuse ; surface covered with subequal, 
flattened, narrow, slightly flexuous ridges, their own thickness apart, separated by flat spaces, about six in two 
lines in the middle of the shell; posterior wing gradually compressed; anal angle 130°; length from beak 
to anal angle one inch eight lines, width at right angles to middle of hinge-line two inches six lines, depth of 
right valve about three and half lines; one or two distant concentric waves of growth near the margin; im- 
pression of a thin lateral tooth extending beneath the hinge-line. 
* Hall says “equivalve,” I suppose by mistake, 
