138 SPECIES OF THE SYSTEMA. 
other, the Mazatlan variety (?), of which I know not a good de- 
lineation, of a yellowish or olivaceous grey, with crowded and 
very concave scales of the same hue. The cited engravings in 
the ‘Systema’ are by no means characteristic, several of them 
being taken from decorticated specimens, whose shape even 
had probably been altered by the polishing-wheel. Argenville’s 
figure probably represents neither of them. As the name can 
only be retained for one of the two, expediency suggests that 
the less known American species should receive a new specific 
epithet (Pacifica, for instance), and margaritifera be bestowed 
on the Chemnitzian form alone. That shell is still preserved 
in the Linnean cabinet, and alone (though many smaller Melea- 
griné are present) answers correctly to the limiting details 
(viridi-fusca, maculis albis, &c.) of the ‘Museum Ulrice.’ 
Mytilus wiguts. 
In the absence of an illustrative figure, even the modern 
genus in which this ambiguous shell should be placed has be- 
come uncertain. No one has yet dared to surmise what our 
author intended. He did not possess it himself: the type was 
in the Royal Museum at Dronningen. From the “ subrotunda 
—juxta basim altero latere inflexa ut Myt. margaritiferus ” 
(M. U.), one is led to suspect that it might have been an Avicu- 
loid Meleagrina ; from the “ cardo margine plano excavatus 
sulcis tribus obsoletis” (M. U.), one might fancy it a Crenatula 
or Perna, but what adult specimen of any of these genera will 
likewise accord with the “longitudinaliter striata, alba, pellu- 
cida”’ of the same work? The division in which we find it placed 
in the ‘Systema’ adds the character “ planus seu compressus” 
to the other details there enumerated. Certain young oysters 
might equally suit the language of the ‘Museum Ulrice,’ but 
assuredly it will be better to wholly omit so indefinite a species 
from our catalogues. 
