84 SYNOPSIS OF THE CHARACTERS OF THE 



AVICULA LAMINOSA. Phil. SP. 

 Gervillia laminosa. Phil. Geol. York. 



Sp.Ch. — Very oblique; ears long, anterior obtusely triangular, jjosterior twice and a half as long as the 

 anterior, forming a lengthened, narrow wing ; posterior side straight, convex ; surface with scale-like Imes of 

 growth. 



This species has the anterior and posterior ears much larger than the A. lunulata; the flat, perpendi- 

 cular space which separates the posterior ear from the body of the shell in that species does not exist in this, 

 the corresponding part being simply convex. Length one inch two lines, width eleven lines, length of hinge- 

 line one inch seven lines. 



AvicuLA LiEViGATA. M'Coy. (PL XIII. fig. 23). 



Sp. C/i.— Depressed, posterior wing about half the length of the shell ; posterior side slightly curved, convex ; 

 anterior side very short, rounded ; an obtuse sinus in the anterior edge ; beak large, prominent, surface smooth. 



This fine shell bears some resemblance to the Gervillia lunulata, Phil, it is easily distinguished by its 

 greater size, smooth surface, and the total absence of the steep, posterior ridge which in that species separates the 

 ear from the body of the shell ; the posterior side is also straighter, and the posterior wing shorter than in that 

 species ; the surface is evenly convex, and quite smooth ; the shell is most convex near the beaks, becoming 

 flatter towards the ventral margin ; the sinus in the anterior side is very wide, but not deep ; there are a few in- 

 distinct lines of growth near the edge. Length two and a half inches, width of hinge-line one and a half inches. 



AviCULA LUNULATA. Phil. SP. 

 Gervillia lunulata. Phil. Geol. York. 



Sp. Ch. — Very oblique, transversely elongate; posterior side arched, defined from the posterior ear by a 

 perpendicular, smooth, flat space ; posterior ear four times as long as the anterior ear ; surface with regular, im- 

 bricating lines of growth. 



This species is rendered very remarkable by the upward curve of the posterior side, which is bounded by a 

 steeply-inclined, narrow space, separating it from the posterior ear, which latter, when well preserved, forms a 

 very long, narrow wing ; the anterior ear is short and rounded ; the surface is marked with regular, imbricated 

 striee. Length one inch seven lines, width seven lines. 



AvicuLA RECTA. M'Coy. (PL XIIL fig. 24). 



S}). Ch. — Convex, obliquely elongate; posterior side straight, obtusely pointed, separated from the poste- 

 rior wing by a broad, steep, longitudinally striated space, nearly at right angles with both the wing and body 

 of the shell; posterior wing half the length of the shell, pointed; anterior wing very short, obtusely pointed; 

 posterior wing and body of the shell girt with sharp, close, regular ridges, parallel to the margin. 



This beautiful species is distinguished from the Gervillia lunulata, Phil., by the sharpness and regularity 

 of the transverse ridges, and thestraiffhtness of the posterior side; the steeply ridged posterior side distinguishes 

 it from the others. Length nine lines, width of hinge-line seven lines. 



AviCULA SQUAMOSA. Phil. SP. 

 Gervillia squamosa. Phil. Geol. York. 



Fragments of this species have occurred very rarely ; they are distinguished by the broad, regular, scale- 

 like striation of the surface. 



