PHOLADOMYA. 



PHOLAUITK. 



sii 



Mr. Griffith* relate* that ihort time after a very violent narth- 

 quake that occurred in Sumatra in the year 1797, which produced 

 " moat tremendous" inundation of the sea, did great damage, and 

 rjoa*d the loea of many live*, these ehelU were procured in a small 

 sheltered bay with a muddy bottom, surrounded by coral reef*, on 

 the ialaoil of Battoo. More than twenty specimens were brought to 

 Mr. Griffith!, but not one wai complete : a portion of the shell with 

 UM apex nearly perfect, and another with the opposite closed extre- 

 mity nearly ao, were however procured. The length of the longest 

 of Mr. Griffiths' shells was 6 feet 4 inches, and the circumference of 

 the base 9 inches, tapering upwards to 24 inches. There were other 

 good one* of smaller sue. The large specimen was nearly perfect, 

 Earing mail part of the lower extremity entire. Most of the shells 

 had adhering to them, about one foot or more from the top, the small 

 cockscomb oyster, small serpuko, &c.; consequently, Mr. Griffiths 

 observe*, they must have been protruded that distance from the hard 

 mod ; but the water being thick and discoloured, the people of Battoo 

 had not taken notice of them antecedent to the earthquake. The 

 specimen* were milk-white on the outside and within were tinged 

 with yellow. Mr. Griffiths remarks that the large end of the shell is 

 completely closed, and has a rounded appearance ; at this part it is 

 very thin. The small end, or apex, is very brittle and divided by a 

 longitudinal septum running down for 8 or 9 inches, forming it into 

 two distinct tubes, inclosed within the outer one, whence the ani- 

 mal throws out tentacula. Mr. Griffiths goes on to describe the 

 substance of the shell as composed of layers having a fibrous aud 

 radiated appearance, covered externally with a pure white crust, and 

 internally a* having a yellow tinge; and the external surface as fre- 

 quently interrupted in a transverse direction by a sudden increase of 

 thickne**, which, he observes, probably indicates different stages in 

 the growth of the shell, although they are at unequal distances, some- 

 time* at 6 inches, sometimes at 4 inches, in the same shell. Many of 

 the shell*, be add*, are nearly straight, others crooked and contorted. 



Trrtio figantta. 



i of shell, giving s front view Into the orifices of the 

 > tab*, sad shoving the IhiekncM of the shell at that psrt ; 2, transverse 

 I of sbtil st UM thickest part sfter It had beta polished, shoving the 

 m, sad gtiing . front rlcw of the orifices Into the double tube. (' J'hllo. 

 .stalisl Tn*Mtlo..') 



PHOLADOMTA, a genni of Conchiferou. Iftthuea, which U thus 

 ********* : Shell very thin, rather hyaline, transverse, ventrioose; 

 inaW* pearly ; posterior aid* short, sometimes very short, rounded; 



U ^T T ui BH *^ rU **< gP">g; PPr '(?e also gaping 

 a little. King* with a small rather elongated triangular pit, and a 

 inarftoal lamina in wch valve, to the outer part of which is attached 

 the rather abort external ligament. Muscular impression, two ; these, 

 a* well a* the mtueular imprvwnn of the mantle, in which there i* a 

 km *im, an indistinct (O. R Sowerby.) 



Tb* pon. />*tod Mr > U a most interesting form, for the knowledge 

 of which we are indebted to Mr. O. a Sowerby, who described it from 

 a recent specie, brought from the island of TortoU by Mr. Nicholson, 

 and in UM posanrion of Mrs. Mawe, from whom it pawed into Mr. 

 Brodrrip collection, and consequently U now in the British Museum. 



The discovery of thi* recent specie, led at once to the more perfect 

 knowledge of several fosails, whose genus, a* Mr. Sowerby observe* in 



his 'Genera' (No. xix.), was before exceedingly doubtful, insomuch, 

 that from a consideration of their external appearance alone, author* 

 had been induced to place them in several genera, to none of which 

 they really belonged as for instance those named Cardila (!) producla, 

 C. obtiua, C. lyrata, C. dcltoidea, and C. maryaritacta ; and Lutraria 

 lyrata, L. ovala, L. antbiyua, aud L. <;nytutala. These occur iu several 

 rocks of the Oolitic Series, particularly the Corubrash, Inferior Oolite, 

 and Fuller' s- Earth ; as well as in the Lias, the London Clay, and the 

 Sutherland Coal-Field ; also in the dark-coloured clay at Alum Bay. 



Professor Owen gives the following description of the animal : 

 " J'holailomya present* all the family characters of the Inctuta, or 

 Eufermds, but differs gonerically from all those, the organisation of 

 which has hitherto been described, by the presence of a fourth aper- 

 ture leading to the interior of the mantle, that is to say, besides the 

 linear slit for the protrusion of the narrow foot at the anterior part of 

 the ventral aspect of the mantle and the two siphonic tubular 

 passages, there is, at the under or ventral part of the base of the 

 united siphons, a small round aperture, which is continued upon a 

 truncated pyramidal papilla projecting into the pallia! cavity, forming 

 a valvular obstruction to the exit of fluids, but admitting their entry. 

 Thia doubtless relates to some curious and peculiar feature in the 

 economy of the mollusc : the foot is compressed, half an inch long, 

 three lines brood; the siphonic tube two inches long, half an inch iu 

 diameter, bifid at the extremity ; the labial appendages short ; the two 

 lirouchiic of each side conjoined, and those of the right united to those 

 of the left side along their posterior fourth. More of the anatomy I 

 have not at present worked out ; but there is enough, I think, hero 

 stated to serve as an answer to M. De Blainville's question." 



P. Candida (G. B. Sowerby) may be given as an example. 



The shell is transversely oblong, very short posteriorly, rounded ; 

 median part marked with divaricated, decussate stria*, which are 

 decurrent from the umbo ; anteriorly elongated, subquadrate. 



It is a marine species, and most probably inhabits deep water. The 

 specimen from which Mr. Sowerby characterised the genus was thrown 

 upon the beach at TortoU after a hurricane. 



This is the only living species, but several fossil forms from the 

 Coal, Oolite, and Lias have been found. 



Candida. 



a, vslves shut, the nmbones towards the spectator ; b, Inside view of valre, 

 hovlng the impressions and the umbo worn through. 



PHOLARITE, a Mineral, a Hydrated Silicate of Alumina. This 

 substance occurs in small pearly scale*, which are usually convex. 

 These are white, soft, and friable, and they adhere to the tongue. 



It occurs in the department of Allier in France, in the Coal Forma- 

 tion of Fins. 



