\ 
MONTAGUE’S BRITISH SHELLS. 855 
of Linnzus; and it is doubted whether 
it is an origimal native of our coasts, or 
become naturalized in consequence of 
being brought by ships from southern 
climates. Like all its congeners, it is a 
borer, and,-in conjunction with the te- 
redo navalis, effectually destroys the 
planks of a ship; the pholas perforating 
across the grain, and the teredo insinuat- 
ing itself with the grain. 
The addition to aay and Da Cos- 
ta’s British species of mya, are, the true 
pictorum of Linneus, found hitherto in 
England only in the river Kennet, above 
Newbury in Berkshire ; the pictorum of 
Pennant, L'ster, Da Costa, and Donovan, 
being a diiferent species, not described 
by Linnzus, is called by Mr. Monta, 
gue ovalis, the ingquivaivis of Walker: 
the pretenuis of Pulteney : sand the sub- 
erbicularis, the distorta and bidentata, 
nondescripts. The first is found in 
hard limestone at Plymouth, and is 
dredged up in Salcomb-bay, detached 
from any other substance, so that it 
seems to be a borer only when it finds 
limestone: the second is found also in 
limestone at Plymouth: the third is of a 
doubtful genus, but as it is more nearly 
allied to the mya than any other, it is 
’ placed there for the present. 
~ As a specimen of Mr. Montague’s 
easy and perspicuous manner in his de- 
scriptions and critica] remarks, we shall 
extract his account of the mya dubia of 
Pennant, with the interesting informa- 
tion contained in his appendix. 
1, PHovapia, 
Mya Dubhia. Br. Zool. t. 44. f. 19.—Turt. 
Lin.riy, p. 179. 
Chama Parva. Da. Costa. p. 234. 
Pholas Faba. Pult. Cat. Dorset, p. 27. 
«« M. with a thin, brittle, opaque shell, ofa 
light colour, and oval shape, marked with 
fine concentric strix: the beak is small, but 
prominent, placel at one end: the valves 
when shut, have a large oval gape or opening 
in front, opposite the hinge. Inside white ; 
hinge furnished with a small plate, or rudi- 
ment of a tooth, projecting inwards. 
at There seems to have been various opi- 
nions with respect to the class in which this 
shell should be placed. 
_ «Mr, Pennant, who first gave it to the 
public, met it in the Poriland cabinet ; and 
seemed to be doubiful with regard to the 
genus in which it ought to be placed, by the 
trivial name of dubia he affixed to it. 
«Ta Costa has placed it with his chama, 
which consists chiefly of Linnzan myx. Dr, 
Pulteney has made it a pholas; we presame 
under the authority of Dr. Solander. It does 
not however appear that there ever were sufli+ 
cient grounds. tor placing it in the pholas ge- 
nus. Even Dr, Pulteney himself remarks, 
that he has seen several of these shells, but 
had not seen one with the accessory valves, 
the essential part of the character of that ge- 
nus. 
«© Mr. Pennant and Da Costa*mention its 
possessing a tooth, or the rudiment of one. 
‘This circumstance perhaps lias more inclined 
us to fix it in the mya genus; others may 
perhaps hereafter remove it to the mytilus; 
for the smiall elevation of the hinge is searcely 
to be denominated a teoth.” 
«« Plentiful at Torbay, in fragments of 
limestone, driven on shore by winter storms, 
but is not to be found in the rocks, which 
are ever uncovered by the lowest ebb tides 5 
and of course is rarely obtained alive: in this 
state, however, we have procured it, and 
proved beyond: doubt, that it cannot belong 
to the pholades, as it is void of accessory 
valves, 
«© The perforations, in which these shells 
are concealed, are sometimes lined with cons 
creted, calcareous substance, closely con- 
nected with the rest of the stene, and equally 
hard, composed of several coats, or lamine, 
of a differegt texture, not unfrequently half a 
line, or mare, in thickness: the openings to, 
these chambers are small, and have some- 
what the appearance of two holes broken into 
one, which is adapted to the shape. of the 
tubes of the animal. 
‘*'Phe whabitant is an ascidia, with two 
very long, slender, white tubes, exceeding the 
leneth of the shell; these are connected to- 
gether their whole length, but terminated by 
two orifices, ciliated with fleshy. fibres, of a 
dark purplish-brown : the body is also white ; 
near the posterior end is a foramen, through 
which, a small foot, or sustentaculum, is 
sometimes protruded, and doubtless the appa- 
ratus, which assists in perforating rocks, 
being always placed in its cell with that end 
downwards, and incapable of turnings 
“<It is probable this, as well as all othes 
similaranimals, whose habits are to perforate 
stone, are provided with an acid, or some sol- 
vent menstruum capable of performing that 
office: it must also he recollected, that this, 
seemingly laborious task, is not affected in 
any given time, but is the work of years ; ag 
the chamber for the lodgment of the animat 
only requires enlarging as the shell erows. 
** Stone of a vitvifiable nature, is impene- 
trable to these animals, but all seach as aré 
wholly, or even partly caleargous, are more or 
less attacked ;* and while this, the mytilus. 
ragosus, donax irus, venus’ perforans,; ang 
* This remark might be attended with considezable national advantage, if pursued with, 
experimen tal ie cated under the direction and encouragement of Government. A coat- 
ing of pounded flint, or glass, laid on timber with a firm cement, would effectually acting 
it from the calamitous ravages of the teredo navalis, and othey animals of similar 
Aabits. 
al4 
‘ 
