ic condition, and it may well be assumed that the
earlier the fusion, the greater the hypertrophy would be. Whether or not
this hypothesis correctly accounts for kyphosis in turtles can be
ascertained only by further study.

Stejneger (Bull. Mus. Comp. Zool., 94: 12, 1944) regards the presence of
8 neurals as opposed to 7 as an important peculiarity of _A. mutica_.
The 42 specimens for which the number of neurals is recorded reveals,
however, that there is greater variation than previously supposed: in 16
_A. mutica_ more than half (9) have 7 neurals and the remainder (7) have
8. Eight neurals were recorded also in 2 of 18 _spinifera_, and in 1 of
7 _A. emoryi_. Seven neurals are present in the single specimen of _A.
ferox_ examined.

It is of interest also that the number of costals, which has been
reported to be consistently 7 in New World species and 8 in Old World
species, varies markedly. In New World specimens, one _A. mutica_ has 7
on one side, 8 on the other, and 8 occur on both sides of one other (of
a total of 16 examined). One of twenty _A. spinifera_, and one of eight
_A. emoryi_ have 8; the single _A. ferox_ (Schneider) has 7. Accordingly
the suggestion by H. M. Smith (Field Mus. Nat. Hist. Zool. Ser., 23:19,
1939) that _Platypeltis_ Baur be resurrected for the American
soft-shelled turtles on the basis of the occurrence of only 7 costals,
is untenable.

The generic allocation of American soft-shelled turtles has varied
considerably in recent years: Smith (_loc. cit._) uses _Platypeltis_;
Pope (Turtles of the United States and Canada, p. 343, 1939) uses
_Trionyx_ Geoffroy; and Stejneger (_op. cit._, p. 8) uses _Amyda_
Geoffroy. As stated above, use of _Platypeltis_ at the present time is
unwarranted, since no constant difference has been discovered that would
support generic separation of Asiatic and American members of this
group. New World turtles should be placed either in _Trionyx_ or in
_Amyda_, depending upon the interpretation of type designation for the
latter name. Malcolm Smith (Bull. Raffles Mus. 3:2, 1930) and others
have considered that, as a part of the original description, Geoffroy
(Ann. Mus. Hist. Nat. Paris, 14:20, 1809) designated the type species of
his new generic name _Trionyx_ as _aegypticus_ E. Geoffroy (=
_triunguis_ Forskal a well-recognized species). Stejneger argues that
Geoffroy did not adequately designate a type from among the many species
he treated in his genus _Trionyx_,