PLANULACEA. 245 



■ columella contiguous to the axis, flat, truncated, and separated 

 from tlie outer lip by a short canal ; outer lip thickened and 

 denticulated within ; operculum horny, thin, with a terminal 

 nucleus. — Obs. This is a genus of small marine shells found in 

 the "West Indies, &c. P. sulcata. PI. xvi. fig. 365. 



PLANE. (Planus.) Plat, planed, as the columellar lip of Pur- 

 pura, fig. 414. 



PLANOEBICULAE. (Planus, flat ; orbis, an orb.) Plat and 

 circular, as Ammonites, fig. 478. 



PLANOEBIS. Mull. ' (Planus, flat; orbis, an orb.) Fam. Lym- 

 nacea. Lam. and PL — Descr. Thin, horny, convolute, planor- 

 bicular, nearly symmetrical ; spire compressed, concave, con- 



. sisting of numerous gradually increasing whorls, which are 

 visible on both sides ; aperture transversely oval, or nearly 

 round ; peritreme entire ; outer lip thin ; inner lip distinct, 

 spread over a part of the body whorl. — Obs. This is a genus of 

 shells abounding in all climates in ditches and stagnant pools, 

 not liable to be confounded with any other, excepting the dis- 

 coidal species of AmpuUaria, which may be distinguished by the 

 aperture being broadest in the opposite direction. It is further 

 to be remarked that the discoidal Ampullaris3 are dextral shells, 

 and the Planorbes are sinistral or reversed ; and although the 



- latter are sometimes so flat and orbicular that it is difficult to 

 know which is the spiral side, it may nevertheless always be 

 ascertained by a careful examination. Possil species are found 

 in the fresh- water strata of the Isle of "Wight, and the neigh- 

 bourhood of Paris. P. comeus. PL xiv. fig. 311. 



PLANOEBULINA. D'Orb. A genus of microscopic Porami- 

 nifera. 



PLANTJLACEA. Bl. The second famUy of CeUulacea, Bl. The 

 . microscopic Poraminifera contained in this family are described 



. as very much depressed, not spiral, chambered, cellular, and 

 having the septa indicated by grooves on the external surface of 

 the shell, which increase in length from the apex to the base : 

 some of the small cellular cavities are to be seen on the margins. 

 This family contains the genera Eenulina and Peneroplis. 



