146 SPECIES OF THE SYSTEMA. 
From the extreme brevity and utter inefficiency of the defi- 
nition of this bivalve, naturalists have been baffled in their 
attempts at recognition. Miiller, indeed, has cited a painting 
of M. Afer in Knorr, as illustrative, but merely from its simi- 
larity to the erroneously cited figure of Argenville. Solander 
has referred to the central H of Gualtier’s ninety-first plate, 
which seems designed for the Modiola barbata. This strangely 
tallies with the circumstance, that the shell, which upon the 
whole answers best of those in the Linnean cabinet (and our 
author once possessed the original) to the description, 1s a worn 
and beardless red-coloured example of that species. In the 
present instance, however, no sure grounded conclusion can be 
arrived at from an examination of his collection. 
From the “ dente brevissimo” of the ‘ Museum,’ where the 
description is unaccompanied by any synonymy, it is probable 
that ruber, whose generic position even cannot be positively de- 
termined from the account in the ‘ Systema,’ belonged to the 
restricted Mytilus of modern conchology ; yet even this conclu- 
sion is somewhat shaken by the preceding passage “ sutura— 
excurrens fere ultra apicem,’ which suggests a Modiola, to 
which genus, indeed, the shell which Linneus eventually set- ° 
tled upon as its representative did actually belong, as is evi- 
denced by the “dens nullus” in his revised copy of the 
‘Systema.’ 
It is probable, then, that the ruber of the ‘Museum’ was dif- 
ferent from the species so named in the earlier publication, 
where the enumerated characteristics are so few that the meagre 
description may be equally applied to more species than one, 
and becomes consequently of no value for purposes of defi- 
nition. 
Is it desirable to retain so ambiguous a species in our cata- 
logues ? 
Mytilus Discors. 
The box thus marked in the Linnean cabinet contains two 
species, Mytilus ( Modiola) discrepans of Montagu’s ‘ Testacea 
