PHOLADOMYA. Sow. (_Pholas_ and _Mya_.) _Fam._ Pholadaria, Lam.--_Descr._ Thin, rather hyaline, equivalve, inequilateral, ventricose, posteriorly gaping, elongated, anteriorly short, rounding; ventral margin rather gaping; hinge with an elongated pit, and lateral plate in each valve; ligament external, short, muscular impressions two in each valve, rather indistinct; palleal impression with a large sinus.--_Obs._ The only recent species of this genus is from the island of Tortola. Several fossil species occur in rocks of the Oolitic series. Fig. 57, P. candida. PHOLAS. Auct. ([Greek: PHôleô], _pholeo_, to lie hid in a cavity.) _Fam._ Pholadaria, Lam. ADESMACEA, Bl.--_Descr._ Transverse, oblong, equivalve, inequilateral, imbricated, gaping on both sides, the anterior hiatus being generally the largest, although sometimes nearly closed, with the dorsal margin surmounted with one or more laminar accessary valves; hinge callous, reflected, with a long curved tooth protruding from beneath the umbones in each valve.--_Obs._ This genus of marine shells, dwelling in holes formed in rocks, wood, &c. is easily distinguished from any other nearly allied genus by the curved, prominent, rib-like teeth. Fig. 55, P. Dactylus; 56. P. papyracea. PHOLEOBIUS. Leach. Part of the genus SAXICAVA, Auct. PHONEMUS. Montf. A genus of microscopic Foraminifera. PHORUS. Montf. TROCHUS agglutinans, Auct. Remarkable for the adhesion of little pebbles, dead shells, &c. to the outer edge of the whorls, which are taken up in the course of the growth of the shell. From this circumstance they are called "Collectors, Carriers, &c." Fig. 360. Recent species are brought from the East and West Indies; fossil species are found in the Tertiary beds. PHOS. Montf. _Fam._ Purpurifera? Lam.--_Descr._ Turrited, thick, cancellated, varicose; spire pointed, generally longer than the aperture; aperture rounded or oval; outer lip having internal ridges, with a sinus near the anterior termination; columella with an oblique fold; canal short, forming externally a raised varix.--_Obs._ The raised external surface of the canal, brings this genus near to Buccinum, while, in general appearance, most of the species more nearly resemble Murex. They have, however, no true varices on the whorls, but merely raised bars. Fig. 416, P. senticosus. PHYLLIDIANA. Lam. A family belonging to the first section of the order Gasteropoda, Lam. The genera belonging to this family may be distinguished as follows: 1. CHITON. Composed of eight valves; valves contingent. Fig. 227. 2. CHITONELLUS. The same, with the valves distant. Fig. 228. 3. PATELLA. Conical, symmetrical. Fig. 229, 230. 4. PATELLOIDA. Differing from Patella in the animal. Fig. 231. 5. SIPHONARIA. With a siphon on one side. Fig. 231*.