I'HiKTHOUSIS 



PHOLADIDA 



316 



utd about < inch** in diameter. It incloses in iu substance a large 

 quantity of farinaceous matter, which the native* use for food in 

 1 tan tr of aoarcity. To procure thi* meal, the imall trunk U split 

 into six or eight pines, and dried and beaten in wooden mortan till 

 tiie farioaoKMM part U detached from the fibre* ; it u then lifted, to 



wpant* them ; the meal u then fit for use. The only further pre- 

 paration which thi* meal undergo** U the boiling it into a thick gruel, 

 or canji. It nami to possess lea* nourishment than common sago, 

 which k obtained in a aimilar manner from another palm, and u lees 

 palatable when boiled, but it has saved many lire* in time* of scarcity. 



PHCETHORN1S. [TBOCUIUDJS.] 



1'HuLADA'RlA, Lamarck's name for a family of Conchiferous 

 Nfllutcm, consisting of the genera Pkolat and Gattroclurna. 



PHOLADID.K a family of Conchiferous Mollmca, embracing the 

 gtotnPlutat.Pkoladid^Xyloplutga.madTtndo. It has the following 

 ebaneten: Shell gaping at both ends, thin, white, brittle, and 

 exceedingly hard; armed in front with rasp-like imbrications; with- 

 out hinge or ligament, but often strengthened externally by accessory 

 valves; hing-plaU reflected over the umbones, and a long curved 

 oceas beneath each ; anterior muscular impression on the 

 pallia! sinus rery deep. Animal club-shaped or worm- 

 like ; foot abort and truncated ; mantle closed in front, except the 

 pedal orifice; siphons large, elongated, united nearly to their ends; 

 orifices fringed; gills narrow, prolonged into the exhalent siphon, 

 attached throughout, closing the branchial chamber; palpi long; 

 anterior shell-muscle acting as a substitute for a ligament. 



The Pkotadida perforate all substances that are softer than their 

 own valves. The burrows of Phoiat are Tertical, quite symmetrical, 

 and seldom in contact. The Ship- Worms (Teredines) also make sym- 

 metrical perforations, and, however tortuous and crowded, never 

 invade each other, guided either by the sense of hearing or by the 

 yielding of the wood. The burrow has frequently a calcareous lining, 

 within which the shell remains free. Teredina cements its valves to 

 this tube when fall grown ; the opening of the burrow, at first very 

 minute, may become enlarged progressively by the friction of the 

 siphon*, which are furnished with a rough epithelium, but it usually 

 widens with much more rapidity by the wasting of the surface. As 

 the timber decomposes the shelly tubes of the Teredo project ; and as 

 the beach wears away the Pkolat burrows deeper. (Woodward.) 



Pkflmi. Animal more or less thick and elongated, rarely shortened ; 

 mantle reflected on the dorsal part, for the purpose of tying together 



sfas4at*X (ulaul a*d aksll) j the lower or ventral parU ore presented 

 , Math; . foot; r, Ub* ; 



Ataal ef W (J.taW ctenta(t), La.), from Ada.wm-.Idc 

 tww, 



,tW; ,*uatl*; *, (got. 



Sbell of rhvlat Dactylia. 



1, Accessory valves : a, anterior pair ; 6, central piece ; r, posterior piece. 

 J, Exterior view of Bhell, side view. 

 S, Internal view of valve : a, spoon-shaped process. 



the valves and the accessory pieces ; anterior aperture rather small ; 

 foot short, oblong, and flattened ; siphons often elongated and united 

 into a single very extensible and dilatable tube ; mouth small, with 

 very small labial appendages ; branchial elongated, narrow, slightly 

 unequal on each side, united on the same line nearly throughout their 

 length, and prolonged even into the siphon. 



Shell delicate, milky white, rather transparent, covered sometimes 

 with a thin epidermis, oval, elongated, inequilateral, gaping posteriorly, 

 and especially at the antero-inferior port ; umbones hidden by a cal- 

 losity; hinge toothless, ligament doubtful; a flat, recurved, spoon-shaped 

 process enlarged at its extremity, elevating itself within each valve 

 below the umbo ; muscular impressions very distant, the posterior one 

 large, oblong, elongated, always very visible, the anterior one small, 

 rounded, but little distinct, both more or less approximated to the 

 edge of the shell, particularly the anterior edge, and joined by a pallial 

 impression, which is long, narrow, and deeply excavated backwards. 



Many accessory pieces or none (?) ; sometimes a calcareous tube 

 enveloping all the parts, but leaving an aperture backwards, (Rang.) 



M. Rang remarks that there ore some species of Pholada which seem 

 to lead to Teredo. These shells inhabit stones, madrepores, wood, and 

 sometimes mud or sand (vase). When the reflux of the sea leaves 

 them, and the animals are disquieted, they eject through their siphon 

 to a considerable distance the water contained in their mantle, and 

 which bathes the gills. ('Manuel de 1'Histoire Naturelle dee 

 Mollunques.') 



Dr. Leach divided the Linnxan Pholada into several genera, but as 

 his distinctions consisted principally in the number of the accessory 

 valves, Mr. G. B. Sowerby has not adopted any of his genera ; they 

 may, according to Mr. Sowerby 's opinion, appear to be calculated for 

 divisions of the genus, but are not sufficiently strong for generic 

 distinctions. Mr. Sowerby admits indeed that some species (Phoiat 

 clarata, Lam., for instance) may, on account of their being closed at 

 both ends, be distinguished genetically, because this circumstance 

 implies a difference in the habits of the animals by which they arc 

 formed : this character therefore, he remarks, has been seized by Dr. 

 Leach, and upon it the doctor founded his genus Martetia, an example 

 which Mr. Sowerby says bo should have been induced to have followed 

 bad be been convinced of its necessity. 



M. Ch. de* Moulins has formed a genus of Pholada which he calls 



M. Rang speaks highly of the discovery of this genus by M. des 

 Moulins, and having studied it with that naturalist, he pronounces it 

 to be very distinct from the Pholadet, and ite place to be clearly fixed 

 between them and the Tertdina, to which it leads so naturally by its 

 valves. Jouannttia, he observes, bus no enveloping calcareous tube, 

 as sometimes happens to the Pholada, tat.; and though only one 

 species is yet known (Jvuannctia wmicavdata, foseil, from the faluus 

 of Merignac, in the interior of madrepores, Ac.), he docs not tbink 

 that a similar tube ever exist*, if the amplitude and disposition of 

 the scutcheon, which appears to him to take its place, is a generic 

 character. 



Mr. Swainson makes the Pholidce the first family of his tribe 

 Macrotrathwt, and thus characterises that family: "Sbell bivalve, 

 sedentary, generally perforating, opening at one or both ends; the 

 valves often prolonged into a shelly tube, sometimes of great length, 

 representing the TubulArancltia." 



Under this family he assembles several forms, and makes it consist 

 of the following genera and sub-genera : 



1. Atptrgillttm ; including the sub-genera AtpergiUum, Ctavaydla, 

 and Fittulana. 



2. Gattrochina (Gautrocluena), Lam. 



3. PhoUuiomya, Sow. 



