Occasional Papers of the Museum of Zoology 29 
smooth forms without mentioning that they differed from the 
main description in this character, it appears likely that he 
did not intend to describe the surface. However, if he did, 
there is intrinsically no more reason for attributing folds to 
his form (a) than to (b) and (c) in interpreting his defini- 
tions. He did not designate either of the forms as a “Var.,” 
as he was accustomed to do where the divergence was thought 
by him to be considerable. Any one of the included species 
could be selected to bear the name “‘crassidens” in a restricted 
sense, but preferably either form (a) or (b) which he pos- 
sessed. A method of dividing species has been provided in 
the International Rules of Nomenclature.t 
“Lea was the first to learn what Lamarck’s species was from 
an examination of the original specimens (Obs. I, p. 199; II, 
p. 125). He definitely restricted crassidens to Lamarck’s form 
(b), which he stated to be the Unio cuneatus Barnes. Whether 
this action was generous or best may be questioned, but he 
undoubtedly had the right to do so under the rules, which 
provide that ‘such designation is not subject to change.’ 
“Lamarck’s description, with those of forms (a) and (b), 
are ambiguous. Experts differ as to what parts of it are intel- 
ligible without knowledge of the types. But, excluding the 
reference to Say’s Unio crassus, which Lamarck did not rec» 
ognize as his own U. ligamentina, it cannot fairly be 
claimed that one of the forms included in crassidens is more 
recognizable than another. Unless the species is to be thrown 
1 Art. 31. The division of a species into two or more restricted 
species is subject to the same rules as the division of a genus, etc. 
(Rep. Zool. Nomencl., Proc. 7th, Internat. Zool. Congr., 1912, p. 47). 
In the division of a genus it is held that “If an author in publish- 
ing a genus with two or more valid species failed to designate or indi- 
cate its type, any subsequent author may select the type, and such 
designation is not subject to change” (op/. cit., p. 46, IIg). 
