8 
THE NAUTILUS. 
characters shading into each other in both regions though perhaps 
less frequently in the Atlantic Appalachian region, so that they 
appear to be in no way related to geographical or environmental 
differences or influences. Size, elevation or depression, color, 
sculpture, etc., are exhibited as might be supposed, in many and 
various facies, but the denticulation of the marginal lip of the 
aperture, or the presence of a tubercular callus or tooth on the 
parietal wall, or a tuberculoid lump or thickening at the base of the 
pillar, all of these last characters are inconstant and variable and 
are often present or absent in examples that are found in the same 
colony, at many if not all places, within the territory inhabited by 
the species of Triodopsis-^-Mesodon group. 
In Triodopsis levettei from Arizona and New Mexico, as well as 
in T. devia-\-Mullani from the northerly region before indicated, 
“ we find all the transitions from tridentate to toothless apertures 
occur.” A comparison between 40 and 50 examples from Cceur 
d’Alene, Idaho, in addition to those previously contained in the 
National collection, indicate that Milliard is but a variety of devia 
as Mr. Binney has placed it 3 ; and to quote Mr. Binney’s remarks: 
“ The variations of this species show very markedly the unsatisfac¬ 
tory character of our so-called genera. Here we have the typical 
devia as a Mesodon, though the variety is a true Triodopsis.” 
DESCRIPTIVE NOTICES OF NEW CHITONS—IV. 
BY H. A. PILSBRY. 
Plaxiphora Suteri, n. sp. 
Shell resembling P. biramosa Q. and P. superba Cpr. ; but girdle 
all over sparcely hairy, without the least indication of pores or sutural 
bristles. Valves smooth, with slight growth-wrinkles, the diagonal 
rib but slightly indicated. Bidge with a chestnut band with a stripe 
of green on each side of it, the pleura and lateral areas uniform 
blackish olive. Girdle blackish with chestnut hairs. Interior blue, 
fading to white on the sutural-plates. Length about 45, breadth 
about 25 mm.; (specimens all curled and contracted). 
Timaru, Sumner and Port Lyttelton, S. Island, N. Z.; (H. Suter). 
A young specimen has the earlier formed portion of each valve 
light brown, spotted with white. This is probably the normal color¬ 
ing of the young shells. 
3 Manual Am. Land Shells, p. 119. 
