482 BRITISH PALAZOZOIC FOSSILS. [ LAMELLIPRANCHIATA. 
Genus. AMBONYCHIA. See page 264. 
AMBONYCHIA VETUSTA (Som. Sp.) 
Ref. and Syn. = Inoceramus vetustus Sow, Min. Con. t. 584, f. 2.= Inoceramus (or Posidonia) vetustus Phill. 
Geol. York. Vol. II. t. 6. f. 3, 4. 
Dese.—Obliquely-ovato-oblong ; beaks narrow, gibbous, prominent, terminal at the anterior end; anterior 
margin, slightly oblique, long, nearly straight, (slightly concave near the beaks, slightly convex towards the ventral 
margin) ; ventral margin semicularly rounded ; posterior side scarcely convex, joining the hinge-line at an 
angle of about 110°; hinge-line entirely confined to the posterior side of the beak, straight, oblique, with a 
slender lateral tooth running below its margin for about two-thirds of its length; right valve deeper than the 
left; both valves most convex near the beaks, gradually arching from thence to the ventral margin, more 
rapidly sloping to the compressed small posterior wing, and very abruptly rounded or sloping nearly at right 
angles to the sides along the narrow, steep, anterior margin. Surface marked with subregular, concentric 
wrinkles, three in two lines at six lines from the beak, gradually increasing with the size of the specimen 
to two lines wide in adults; obscure parallel concentric lines of growth visible on some specimens. Width of 
very small example from beak to ventral margin one inch, proportional length of anterior slope, measured from 
the beak towards the ventral margin * to 4%, length of hinge-line 44 to ,%., greatest length from a little below 
the middle of posterior side to opposite point of anterior side %, depth of left valve about %, depth of right 
valve =, (adult length about two inches). 
Our specimens of this species are very small and ill-marked, but one of them is particularly valuable for 
shewing for the first time the nature of the hinge, and that it has no relation to the genus Jnoceramus on the 
one hand, nor to Posidonia on the other, but it is really a one-eared Avicula of the remarkably thick-shelled 
genus Ambonychia of Hall. 
Position and Locality —Carboniferous limestone of Kendal, Westmoreland. 
Genus. STREBLOPTERIA (A/'Coy). 
Etym. orpeBr0s, perversus ; and mrepiv, ala. 
Gen. Char.—Ovate or rounded, obliquely extended towards the anterior side; posterior wing broad, un- 
defined, nearly rectangular, extending nearly as far as the posterior margin of the shell; anterior ear small, 
deeply defined ; surface smooth, or radiatingly ridged; one large, faintly marked, muscular impression a little 
behind the middle; one short, narrow, tooth slightly diverging from the hinge-line on the posterior side of the 
beaks ; ligament confined to a narrow, simple facet on the hinge-margin. 
These shells differ from some of the short-winged group of Avicula (or Pteria), to which they are most 
allied, by the obliquity of the body of the shell being towards the anterior instead of the posterior side—the 
reverse in fact of what occurs in nearly all shells except the Zima. There are many species in the carboniferous 
limestone, to which the genus seems at present confined, unless the Pterinea posidoniiformis (M°Coy) of the 
Upper Silurian belongs to it. 
STREBLOPTERIA LAVIGATA (J/°Coy). 
Ref. and Syn. = Meleagrina laevigata M*Coy, Syn. Carb. Foss. t. 12. f. 5. 
Dese.—Suborhicular, oblique, evenly convex, greatest depth a little above the middle, smooth ; posterior 
ear undefined, slightly more than rectangular (110°), rather less than half the length of the shell long; anterior 
ear very small, square, deeply divided from the body of the shell by an abruptly curved slope ; anterior margin 
much more convex than the posterior, forming, with the front and part of the posterior side, nearly three-fourths 
