294 The American Geologist. '^^^^'- ^^^■*- 
panied the first generic diagnosis ; and finally the statement 
is made in so many words that it was this species which tauglit 
the author the generic difference from Pecten, hence the name. 
It i? absolutely certain, therefore, that A. docens was the form 
upon which the genus Aviculipcctcn was based. Were it not 
for a fact to be mentioned later, an objection might here be 
raised against employing this species as the genotype, on the 
ground that a generic name proposed must be associated with 
some typical species, while A. docens was not published until 
four years after the description of Aviculipcctcn. It might 
be urged, on the other hand, that as A. planiradiatns and .4. 
rut live ni are unquestionably not the species upon which Avic- 
ulipecten was really based, neither of them can with any 
propriety be made the type ; that the genus being without a 
type at the time of its proposeal is invalid until the descrip- 
tion of A. docens in 1855 placed it upon a proper footing, and 
that it can be regarded as only then having been properly 
established. Such an academic argument, however, is not 
necessary, for from the synonymy preceding the specific de- 
scription and the remarks following it, it is clear that A. 
docens is .not a species newly described, but a new name sul)- 
stituted for Pecten tle.vuosns which was published by AlcCoy 
in 1844, the name having been preoccupied by Pecten flex- 
uosus Lamarck. Thus the discrimination of the species upon 
which the genus Aviculipecten was based dates from 1844, and 
antedates the generic description by seven years. As to the 
name of this type species, since Pecten fie x uosus Lamarck 
is a living form, and certainly not an Aviculipcctcn, it does 
not conflict with Aviculipcten llcxuosus McCoy, except so 
far as one adheres to the dictum "once a synonym always a 
synouMU." While for my own ])art I am disposed to retain 
the older name Hexnosus, others doubtless will use docens for 
the species, which has a clear right to be regarded as the type 
of the genus Aviculipecten. The discrimination of the typical, 
however, among the several species used by different writers 
is of little practical importance m the present case, because 
all are so similar in general appearance as to establis'.V the 
probability that they are congeneric, and it may have been 
merely a dift'erent conception of the synonymic relations of 
these s]>ecies which led \\'()()(l\\ard. usually very precise in 
