76 
KEPORT—1847. 
variable iraportance In the different tribes. The general habit, and ofteo thescilf- 
tore of the shell, are usually in striking accordance with the roost esseotialfeatiRs 
of the animal. Characters derived from the hinge and from the position of ihelia- 
rncnt, hitherto raaiiilv depended upon by couchologists, prove to be in the najoritr 
iJ”***°5** guides for determining the natural affinities of the inoUtBhanil 
•eidom of more than generic value. 
The following are the families adopted by the authors:— 
SecliuD A. Dinyarin. 
1. PfiotADtD.«— including T'emfo, Pftolaa and Ga$frochana, as typ«s of tebe, 
last associated with Saxicava ami I'cHfrvjns, and probably Ae<ero, Poro*yi»iiil 
p tnxft. Animal with a mantle ctoi&cii in front, leaving a small antsalaperturtlbf 
c pass^e of the truncate or digitiforin foot. Siphons united nearly to iheirsitff- 
mities, their apertures cirrated. 
2. Myad.® including Mya, J^anopaa, Lutraria, and perhaps Coriido. Mutfc 
c 08 C( except anteally, where it is open for the passage of a thick and dsiilbnii, 
u 'uut. Siphons long, united to their extremities (which are slifbtlf 
tjinlirmted). inclosed in on epidermic sheath. 
».oil' 0*" which Solen is the only British genus. Mautle closed except aa- 
rLri *3 open for the passage of a vciy large, thick, nMiquelytnuwte 
partly limbriiUcd. Siphr'ns abort, united im- 
equal with cirrated margins. f ' 
niW Mantle open anteriorly for the laige, thick, api- 
nn/i •*** c t “u enlarged, united base, divided at their KSeoiBes, 
and having fimbriated apertures. 
„J,' M.autle open for a falcate foot. Siphons unequal, partly 
umu^ and divergent, with fimbriated apertures. Pamlora, Loma. 
or U fimlrriated at the margin. Foot digiti/win 
turo* septu-ated, often nearly equal, and having plainiprf- 
7V2/ia‘n Aforttavvfa} form one section of this groip; 
vewmo arid a second and more typical division. 
lar ' open, fimbriated at the margin. Foot broadly triacji- 
an.i probably at the edge. Ponax and Maodm. 
to the^*«^ncrt« r ojien, fimbriated at the margin. Siphons united owlf 
witli th.. ® Foot triangular. Afeefro links this grtwp 
9^. <>P« afare typical.^ 
so • oRf. win. . , open, fimbriated. Siphons very short, nnited. or seuif 
io “"!'>riated, the otlMr plaiel C,p-i»a. A^url,. Bttt. , 
very short nnitn.!’ ^^P®*** fi“briated. Foot hamate and digitiform. SipboB* 
CwJrf??* ' ''‘eir >'“‘15. Apertures, one plain and one 
briated shffi^noi'^nA ^osed, except a small aperture for the foot and two fi»‘ 
12. Foot hamate. Isocardia. 
foot, which is Sh-nder nnH* r P"’^» leaving an opening aateallrfor^ 
ob«ilete; bothapertu!^s^iI}'^'^^'’T‘' • “nedoal. one bemgoftenM 
nearly stssilf nuL closed, except a small aperture for tbe foot and ^ 
openings. Ac/«e. Gah^mc? Lepi^r . ^ 
oh-vcilete. Foot vAr« t ^ Siphons very short, fimbriated, "• 
15 Drri "™ targe. I’nio, Atiodon. 
foot digitifi)rm ''*^pi*g^^**^*^ great portcloscd. Siphons very short, fi®briw» 
»iphQn».*'^Iw°f' ^‘*”1’® “pon- and not closed, or only partlv closed. » 
uuu uui ciosea, or only partly cioaru. 
M »i 5 and in an allied group,and Jrrt*®- 
then united. Fool dl^ifonn^*** °r considerably developed- 
v^/•ca, Pectunadua, Leda, Amck/a. 
!*• Frctkmd* m .1 ^tion B. Monomyaria. ^ 
'^lo^d. Pt^ctan. Lima^ completely open, fimbriated and eyed. Foot well-*- 
•'D«. Mantle freely open. Foot obsolete. Osirea, Monia. 
