326 Dr. H. A. Pilsbry on the 
group; (10) it is premature to follow the strict rule of 
priority when the earliest name was based upon a species 
not positively known to belong to the genus as built up ; 
(2) the rule of giving page-priority in the case of two or more 
names for the same group, appearing in one book, he does 
not recognize, but would select the supposedly most typical 
from among such names; (3 & 4) after discussing the 
question of names applied to composite groups, such as those 
of almost all old authors, Dr. v. Méllendorff states that he 
considers a generic name preoccupied only when a prior 
homonym is actually in use. 
To these proposed exceptions to the strict rule of priority 
I would reply that any exception gives opportunity for those 
individual differences of opinion which it 1s the sole purpose 
of rules of nomenclature to obviate. Exception (1a) opens 
the door to endless discussion as to what is or is net an 
aberrant species. ‘lo my mind the examples cited by von 
Mollendorff are not such. Thus, Helicigona lapicida is 
typical of its genus in soft anatomy, and aberrant in a single 
character of the shell alone, i.e. the carination. Is a specific 
character of this sort enough to cause us to disregard the 
rule of priority? And, then, who is to decide upon what is 
the natural type of a genus? for here theoretical consider- 
ations will rule. I grant the force of the objection no. (1 8) ; 
it applies, however, to no Huropean Helicide. Regarding 
exception (2) it should be said that if page-priority be 
rejected there is absolutely no rule to cover cases of two or 
more names for one group in one book. I therefore hold 
that, as Jordan says, “in case of twins, primogeniture con- 
trols.”” Objection no. (4) seems to me to be wholly im- 
possible of application. How are we to tell whether a name 
proposed in Coleoptera, for instance, will not become a valid 
genus, even if now temporarily relegated to synonymy? We 
are constantly taking up and using names long supposed to 
be synonyms. ‘The concrete cases discussed by v. Méllen- 
dorff are as follows :— 
Xerophila, Helicella. 
This is a case of unusual difficulty, from the fact that all 
the early authors placed the species of the modern genus in 
company with many really diverse forms. Whether I took 
the best course in using the name Helicella remains open to 
doubt. At all events, the supposed use of that name, prior 
to Férussac, alleged by von Mollendorff, is easily disposed 
of. In his ‘ Extrait du Cours de Zoologie,’ 1812, p. 115, 
Lamarck enumerates the genera of Colimacés—Heélice, 
