32 SYNOPSIS OF THE CHARACTERS OF THE 



TUREITELLA TENUISTRIA. Phil. 

 Turritella tenuistria. Phil. Geol. York. 



Sp. Ch. — Acutely conical; whorls flat, slightly angulated below; surface with very fine, oblique, and 

 spiral striae. 



This abundant species is easily recognized by its conical, tapering form, and plain, slightly striated volu- 

 tions. Length one inch six lines ; diameter at base seven and a half lines. 



Tuhbo. Linn. 



Gen. Ch. — Tiu-binate, ventricose ; spire pointed ; aperture round, entire ; base convex. 



Turbo spirata. M'Coy. (PL V. fig. 29). 



Sp. Cli. — Ovate ; spire lengthened ; acute, conic of about five slightly convex whorls ; basal turn, small, 

 ventricose, rounded, imperforate ; aperture ovate, rounded anteally ; pointed retrally, rather more than half the 

 length of the shell. 



Only casts have as yet occurred of this species, which differs from the Buccinum imbricatum, Sow., in the 

 small size of the basal whorl, and greater length of the spire, and number of the volutions. Length one inch 

 and, probably, seven lines ; diameter of last whorl one inch three lines ; length of the mouth eleven lines. 



LiTTORiNA. Fer. 



Gen. Cli. — Turbinate; spire small, accuminated; aperture large, rounded anteally ; outer lip sharp ; pil- 

 lar lip flattened. 



The recent Littorinm, as their name implies, are found chiefly on the shores, or in shallow water, where 

 they feed on the sea-weeds. 



LiTTORiNA pusiLLA. M'Coy. (PL V. fig. 26). 



S}). Ch. — Ovate, short; spire small, sharp, of three convex whorls; surface smooth; mouth rounded an- 

 teally, narrowed retrally. 



This is one of the smallest species of the genus found in the Carb. limestone ; the spire forms rather less 

 than a third of the length of the body whorl ; aU the whorls are convex, and the surface quite smooth. 

 Length three lines, width two lines and a quarter. 



Lacuna. Turt. 



Gen. Ch. — Shell globose, thin; body whorl large, ventricose; spire very small, pointed, of few, rapidly in- 

 creasing whorls ; aperture semicircular ; columella obUque, the upper part reflected over the umbilicus, which 

 forms a lengthened groove behind the columella. 



Lacuna antiqua. M'Coy. (PL V. fig. 24). 



Sp. Ch. — Depressed; volutions rounded; spire very small, acute, of three rapidly enlarging whorls; um- 

 bilicus very large, sharply defined ; inner lip slightly reflected over it above, oblique ; aperture large, semicir- 

 cular ; surface very finely striated across the volutions. 



This curious little shell seems to be the first instance of the genus Lacvna occurring in the older deposits. 

 The drawing has been injured in the lithographing. Length two lines, diameter three lines. 



