914 The American Naturalist, (Norah, 
to in passing. In the first place, those species which have a 
very extended mantle, with hardly an exception have a lirate 
aperture (Oliva, Olivella, Cypræa, Trivia, etc.). With species 
in which there is a widely extended mantle and yet no lira- 
tions, it will usually be found that the mantle is not entirely 
withdrawn into the shell in such forms, or is permanently ex- 
ternal to the shell (many Opisthobranchiata, Marseniidz, Sigare- 
tus, Harpa, etc.). In a group, like the: Cyprzide, where nearly 
all the species are lirate on both lips, there are a few which 
want these lirz, and these are species which have a wider aper- 
ture in the adult than most of the genus, and in which we 
should expect the wrinkles to be less emphatic. 
