LUCINOPSIS. 135 
to the Veneride, as none of the genera of the latter family 
have any resemblance to this siphonal condition; still it cannot 
be lost sight of, that the three primary teeth in the left valve, 
which appear in no tribe but in that of the Veneres, give it a 
decided connecting link with them. 
As to the alliance of Lucinopsis with Lucina, it is not very 
near, and principally consists in its lenticular shape, which, 
however, is that of many of the Veneres, so that a less signi- 
ficant appellation might have been preferable. I must likewise 
observe, that there are some differences of shape and position 
from either the Telling or Veneres in the adductor cicatrices 
of Lucinopsis, which have a slight approach to the Lucine ; 
in other respects there is little in common between the two, 
there being no siphonal apparatus, and a very peculiar foot in 
Lucina. 
These remarks may induce malacologists to take into con- 
sideration, that, the Tellinide and Veneride being so closely 
allied by the intervention of Lucinopsis, it would be desirable 
to remove Mactra into the vicinity of Cyprina, to precede it 
and follow Cardium, in which case the line would march thus : 
—Cardiade, Mactride, Cyprinide, the Veneride, then the 
Donacide, the Tellinide, and their genera, &c.; and thus, by 
relieving the Tellinide and Veneride of the imtermediacy of 
the Mactre, perhaps a greater approach to a natural position 
would be obtained. 
The peculiar characters of the shell of Mactra create a diffi- 
culty with respect to natural order, as it has many features of 
the Myade and Anatinide ; but the open mantle of the animal 
will not allow it to be so near a neighbour to them as to follow 
the Tellinide ; neither can it remain between the latter family 
and the Veneres, the union of which, I think, is more naturally 
effected by Lucinopsis, notwithstanding the anomalies that 
exist in that genus. The siphons of Mactra are altogether 
different from those of the Telling ; their tubes are more con- 
gruous with the Veneride, so that it might have been placed 
immediately after the typical Veneres if the Cyprinide had not 
intervened, which, however, cannot be severed from them, 
merely because their siphons are so short as scareely to pro- 
