PARTULA. Fer. _Fam._ Colimacea, Lam. Auriculacea, Fer.--_Descr._ Conical, smooth; spire equal to the aperture in length, consisting of few whorls; aperture auriform; outer lip reflected, broad; inner lip reflected, with a slight prominence on the columella. P. australis, fig. 302. PASITHÆA. Lea. A genus formed of some pyramidal shells, described as resembling Melania, but separated from that genus on account of being marine fossils. Fig. 317, P. striata. PATELLA. Auct. (_A dish_ or _platter_.) _Fam._ Phyllidiana, Lam. Retifera, Bl.--_Descr._ Symmetrical, compresso-conical, nearly regular, oblong or oval; apex sub-central, inclining towards the anterior margin; aperture oval, forming the base of the shell; internal surface smooth; with a muscular impression shaped like a horse-shoe, with the ends bending forwards, encircling and dividing the space all round, except where the interruption occurs to receive the head of the animal; external surface ribbed, grooved, striated or banded radiately. On rocks and sea-weeds in all climates.--_Obs._ Patelloida differs from Patella in the construction of the animal; Siphonaria, in the lateral siphon; and Ancylus, in the oblique twist of the axis, as well as in the nature of the animal. The Patellæ are marine. Fig. 229, P. Oculus. PATELLIFORM. (_Patella_, a dish; _forma_, shape.) Shaped like a dish, or like shells of the genus Patella. PATELLOIDA. Quoy and Gaimard. LOTTIA, Gray.--_Fam._ Phyllidiana, Lam.--_Descr._ Patelliform, rather flat; apex obtuse, leaning towards the posterior margin; muscular impression not symmetrical, but widest on the right side near the head of the animal; central disc of a variable brown colour. On rocks and sea-weeds in all climates.--_Obs._ The shells of this genus so closely resemble Patella that it is almost impossible to make the distinction from the shells alone. They are, however, generally flatter, and have the apex placed somewhat nearer the posterior margin. The animals are very distinct. Fig. 231, P. Antillarum. PATELLOIDEA, Bl. or patelliform shells. The third family of the order Monopleurobranchiata, Bl.; the animals of which are described as depressed, flattened, covered by a wide external shell, which is patelliform and non-symmetrical. This family contains the genera Umbrella and Siphonaria. PATROCLES. Montf. A genus of microscopic Foraminifera. PATULARIA. Sw. A sub-genus of "Anodontinæ," Sw. thus described: "Shell nearly equilateral, round or cordate; no teeth. P. ovata, Sw." _Ex._ _Conch._ pl. 36. rotundatus, Ib. pl. 137. PAVONIA. D'Orb. A genus of microscopic Foraminifera. PAXYODON. Schum. HYRIA, Lam.