472 ©. A. Young—Diffraction Grating for Solar Spectroscope. 
from the smallest to the largest sizes; but the former some- 
times becomes plain-colored before reaching maturity. There 
is no evidence that Natica clausa is the Nerita affinis of Gmelin, 
but quite the contrary ; for the latter was placed in the section 
of umbilicated species, was described as silvery within, and came 
from New Zealand! It is probably one of the Trochide, and 
certainly could not have been this imperforate Natica. 
In this place I shall not enter into a discussion of the numer- 
ous cases in which the author has reduced the American shells 
to ‘varieties’ of the European species, because in many 0 
these cases there must long be great diversity of opinion, and 
for most purposes it matters little whether these closely related 
forms be called “ varieties” or “species,” so long as the actual 
differences are recognized. But since Mr. Jeffreys has evidently 
made so many important mistakes in his article in regard to 
the identity of species, and has united those that have no near 
nities, as already shown, it is logical to conclude that he 
may have made other mistakes in the case of more critical 
species. He must therefore pardon us if we regard his decisions 
in all these cases as at least doubtful, until confirmed by other 
evidence. | 
Art. LIL—WNote on the use of a diffraction “grating” as a substi- 
tute for the train of prisms in a Solar Spectroscope; by Prof. 
C. A. Youne. 
prism of 60° belonging with the original instrament. 
