M Y A 
of the hinge with a fubulate proje&ion near the primary 
tooth ; that of the other valve dilated. It is found in 
the rivers of Guinea. 
23. Mya nitida : ihell oval, white, fuiooth ; with an 
obtufe tooth in each hinge. It inhabits Norway. 
24.. Mya membranacea : Ihell ovate, membranaceous, 
white, with a p rot rafted reflected margin'at the probolcis. 
25. Mya byllifera : Ihell coarfe and thick; oblong, ftri- 
ate, convex ; hinge without a tooth. It is found in the 
ft flutes of rocks on the Greenland coafl, and is generally 
found affixed by a byffus, or mafs of filaments. 
26. Mya dubia : ihell with an oval and large hiatus op¬ 
posite the hinge, and the rudiment of a tooth within one 
valve. It is found near Weymouth. The ihell is brown 
and brittle; the length of a horfe-bean, and ihaped like 
a piftachia-nut. 
New Species from the Linnaau Tranfafl ions. 
Several varieties of the two following fpecies, with other 
new fpecies of teitacea, which we (hall hereafter have oc- 
caiion to notice, were referred to Dr. Mafon, V.P. L. S. 
by fir Jofeph Banks, bart. who received them from the 
reffuary of the Rio de la Plata. Dr. M. in the introduc¬ 
tion to his description of them in the Linn. Tranf. vol. x. 
observes ; “ It is Angular that fo many new fpecies fliouhl 
have been found collected together in one (pot; and ilill 
more fo, that no one fpecies before defcribed fhould have 
formed part of the aflemblage. I am induced to think that 
they were brought down together by home of the tributary 
ftreams of the Rio de la Plata, from interior parts of the 
South American continent not hitherto explored by con- 
chologifts ; the name of one of thefe ftreams proves that 
it abounds with natural productions of this tribe, for it is 
called Rio di Conchas-, or River of Shells. Many of the 
bivalves were found enveloped in the gelatinous matrix 
(if it may be fo denominated) in which they were ftrft 
deposited, and to which probably all teftaceous creatures 
remain attached (unlefs removed by mechanical violence) 
until the calcareous covering which is to form their pro¬ 
tection has acquired the requiiite degree of firmnefs. In 
the prefent initance, this matrix, in itsdryftate, forms a 
tough, but thin, femitranfparent iubftance, not unlike 
bladder in texture, and foluble in nitrous acid. The 
young (hells are attached to it by their epidermis, which, 
in faft, feems to be merely a membranous expaniion of the 
fame fubftance, and to take its origin from it for the pur- 
pofe of confining the animal during the formation of the 
ihell. In fome ipecies, the attachment of the membrane 
is fo loofe, that it is thrown off very foon after the animal 
is fet at liberty; but in others it remains firmly adhering 
to the calcareous matter during life. Mod ftuviatile ihells 
retain this covering more or lefs entire, and it is the cafe 
with all the fpecies hereunder defcribed, in all their ftages 
of growth. The membrane by which the calcareous mat¬ 
ter of the ihell is fecreted, or depofited, is of a very dif¬ 
ferent nature, and has a more immediate connexion with 
the contained animal.” 
27. Myalabiata: ihell fuboval, firm, tranfverfely ftri- 
ated, green, of a pearly brightnefs .within ; valves clofe, 
the margin of one of them projecting over the other like 
a lip; hence the name.. Fig. 1, 3, 3, on the annexed 
Plate, are different fpecimens of the fame fpecies : they 
are in general about an inch in length, and rather more 
than half an inch in width. “ It is one of the mod re¬ 
markable bivalves with which I am acquainted, part of 
the margin of one of the'valves projecting over the cor- 
refponding part of the other, fo as exaCtly to referable a 
lip. It is fortunate when fo linking a character prefents 
itfelf, for the fpecies cannot, in fuch circumftances, be 
miftaken.” 
28. Mya variabilis : ihell fubrhombic, gibbous, with 
rough prominences lengthwife; dark-green; valves with, 
two teeth, diverging at top ; the interior of a pearly 
brightnefs with a caff of blue. Inhabits with the laft: 
one inch long, and the fame in breadth. The young (hell 
Vol. XVI. No. 1124. 
M Y A 4Sf) 
is lefs gibbous, fubrhomboidal, brittle, ahrsoft tranfpa-. 
rent, purpliih within, with many rugoiities reaching near-- 
ly to the margin. 
“ This ipecies varies extremely in its ftruCture and con-: 
tour, according to its feveral ftages of growth ; and, if I. 
had feen only the youngefc and the oldeft (hells, without! 
having had opportunities of comparing thofe of interme¬ 
diate ages with each, I fhould mod probably have given, 
them feparate places in the genus. See'fig. 4, 5, 6, 
There can be no doubt that many other teitacea (efpe-> 
cially in the genera of Mya and Mytilus), at prefent con-, 
ftdered as diftinCt fpecies, will, from the occurrence of 
fimilar opportunities, be found to owe their difference of 
form folely to difference of age. The molt: ftriking cha¬ 
racter in the younger fpecimens of. Mya variabilis is the 
radiating rugic, or plaits, which proceed from, the apex 
of the umbones, and cover nearly the whole of the ihell. 
In fig. 6, it will be feen. that the ruga, though fo ftrong 
over the whole of the younger ihell, fig. 5, are very in- 
diftinCt as they pafs towards the margin ; and in fig. 4, 
the oldeft of the three fpecimens, they are almoft obfolete, 
except on the decorticated umbo. It will be remarked 
alio, that the outline of the (hell becomes totally different 
at its full growth, gradually verging from a fubrhom¬ 
boidal, or i'omewhat obliquely oval, to a fubrhombic or 
almoft orbicular form. As thefe differences are fo marked, 
no perfon, I conceive, who duly confiders the facts, which- 
I have mentioned, will be liable to feparate Mya varia¬ 
bilis into feveral fpecies.” Linn. Tranf. vol. x. p. 325-8. ■ 
29. Mya ftriata : (hell fub-pellucid, white, of a delicate 
texture, finely ftriated longitudinally; the lhape is fub- 
parallelogrammic ; the anterior end is truncated, and the 
valves refieCt, forming a hiatus when the ihell is doled; 
the pofterior end is rounded ; the umbo is fmall, and 
placed neareft the pofterior end. The iniide is white, and 
{lightly reflects a nacred hue; the hinge' is Ample, pof- 
felling one ereCt broad tooth in one valve, that locks into 
a correfponding cavity in the other. Length half an inch ; 
breadth one inch. This new fpecies, it appears, was firlt 
difeovered by Mr. Lyons in Tenby-bay, on the fouth 
coaft of Wales; and feveral more have been fince taken 
by the fame gentleman aftera florin, which were all alive. 
The i’pecimen firlt fent was communicated by Mr. Mon¬ 
tague, author of Teitacea Britannica, to the Linntean 
Society, and defcribed in their TranfaCtions for the year 
1815. This fpecies is Ihown on the annexed Plate, at 
fig. 8. and the tooth at fig. 9. Mr. Montague, adds, 
“ Round the anterior end of my fpecimen there is a por¬ 
tion of agglutinated fand, which induces an opinion that, 
like molt others of the fame genus, it refides imbedded in 
the fand at the bottom of the fea." (Linn. Tranf. vol. xi. 
p. 188.) And it is now.a prevailing opinion, from certain 
obfervations on the growth of thefe Ihells, and the num¬ 
ber of their annual laminae or fcales, that this fifli will 
attain to a great age, and that fifty or ftxty years is but 
a very moderate computation. Linnaeus has Ihown that 
' the Mya will bear removing, and that, by a particular pro- 
cefs, it may be put intoaftateof producing pearls at plea- 
lure in the relervoirs to which it is transferred, the old 
pearls being removed to make way for the formation of 
new ones. 
MY'A, in geography, an illand in the Eaft-Indian Sea-, 
about ten miles long and four broad. Lat. 1.14. N. Ion. 
127. 27. E. 
MYAGROI'DES, f. in botany. See Draba. 
MYA'GRO SIM'iLIS. See Erysimum and Mya- 
GRUM. 
MYA'GRUM,/ [a word adopted from Diofcorides, 
whole neverthelefs is very oblcure, nor does that 
author lay any thing which may lead to the meaning of 
the name ; except indeed that he deferibes the plant as 
making a rude lort of candles: “The fat feeds, roafted 
and bruifed, are fmeared over the twigs, which then,” 
fays he, “ ferve in the place of lamps.” Such artificial 
lights are well known to attract flies to their deftriRtion ; 
5 K- and 
