INTRODUCTION. 5 
perfectly coincides with the diagnosis as further defined by the 
cited delineation. In consequence, however, of the addition to 
the original examples which has formerly been deplored, one is 
frequently baffled, after an infinity of pains-taking, through the 
parity of pretensions exhibited by the two or three final 
claimants (the residuum of the analysis) to the specific appella- 
tion. Where the balance of conflicting testimony is even, 
tradition (the general assent of authors to a supposed identifi- 
cation) should have due weight in the preservation of established 
names. 
Locality, that great auxiliary in ascertaining the names of 
modern species, may also be taken into account, but its im- 
portance must not be overrated, since, in the infancy of Natural 
History, few objects, on their reception into a museum, were 
supplied with due credentials as to their nativity. The locali- 
ties mentioned in the ‘ Systema” were usually drawn from the 
works referred to in the synonymy, and must stand or fall with 
the synonyms themselves. Shells described originally, like- 
wise, without any habitat appended, may occasionally have 
received a false one in the final edition, from an erroneous im- 
pression of their identity with others subsequently received 
from a known quarter. Nevertheless the locality will often- 
times guide us to a correct conclusion, as in the case of species 
indigenous to Sweden, or such as are authenticated by Brander 
(the Consul at Algiers), Zoega, &c. Moreover, since we now 
possess a tolerable knowledge of the geographical distribution 
of the J'estacea, the occurrence of any specimen from a land 
unvisited before the year 1766 would throw the greatest doubt 
upon its typical claims. The published and unpublished cor- 
- respondence of our author reveals some of the sources from 
which he drew his collection. 
In former days the most recognisable figure of those cited 
by Linneus was selected as typical, little regard being paid to 
the description. The reverse of this facile process is now ac- 
knowledged to be correct, the figures being subsidiary, and only 
of authority when in accordance with the diagnosis, and then 
chiefly as further defining the species by contracting the too in- 
clusive characters which result from the brevity of style affected 
by our author: for in the event of not finding among his books 
an accurate representation of a shell (at that period many were 
