68 THE NAUTILUS. 
tralian species—G. petterdi and beddomei. It is nearly allied to 
Ancylus, from which it differs anatomically by a distinct pattern of 
radula, and conchologically by its compound shell. The existence, 
variously affirmed and denied, of a jaw, is now demonstrated by fig- 
ures. It has been suggested, but not proved, that in unfavorable 
circumstances the shell never attainsits compound development, but 
remains simple. From an Ancylus of the same size the subcentral 
nucleus and regular elliptical outline distinguish young Gund- 
lachia. 
A fuller knowledge of the development and structure of the 
genus is very desirable. 
The nearest, in phylogenetic array, to Gundlachia are probably 
the New Zealand Latia and the Tasmanian Ancylastrum. Should 
Hutton’s Latiide win acceptance, which seems doubtful, it might 
include these. 
The distribution of Gundlachia agrees in part with that of the 
recent marsupials, and the theory of a Mesozoic or older Tertiary 
migration to or from Australia across the south pole, when a lost 
land with a mild climate united Tierra del Fuego to Tasmania, 
would explain its present position. 
A NEW MEXICAN BYTHINELLA. 
BY HENRY A. PILSBRY. 
Bythinella palomasensis. 
Shell small, ovate, rapidly tapering above from the periphery of 
body-whorl to a blunt apex ; composed of four very convex whorls, 
the last about five-sixths the entire length of the shell, well rounded 
out. Surface showing faint growth-wrinkles only. Aperture ovate, 
subangular above, its longest axis about half the length of the shell ; 
peristome thin, continuous across the parietal wall and nearly 
straight there, although not appressed to the body-whorl. Umbili- 
cus minutely perforated. Color whitish corneous and somewhat 
translucent. 
Alt. 2°75, max. diam. 1°80 mm. Longer axis of aperture 1°36 mm. 
Two specimens from Lake Palomas, northeastern Mexico, col- 
lected by Dr. E. A. Mearns, U.S. A., of the International Boundary 
Commission. One of the two specimens has the latter third of a 
