LYMNZIDZ OF NORTH AMERICA. 295 
than humilis, with shouldered whorls and a larger aperture in com- 
parison with the rest of the shell; the aperture is also larger and 
rounder in galbana. Obrussa decampi has a superficial resemblance, 
but is a much narrower shell with elongated aperture and squarely 
shouldered whorls. The inner lip is also differently appressed than 
either humilis, modicella or decampi. Galbana may be known by its 
solid shell, its swollen and somewhat shouldered last whorl, its short, 
generally dome-shaped spire and its broadly reflected inner lip which 
emargins the umbilical chink. The spire varies somewhat in height, as 
does also the aperture. (See plate XXXII.) In the Michigan speci- 
mens the sutures are not as much compressed as in the New Jersey 
specimens. 
Like its congener, Galba obrussa decampi, galbana lived in the icy 
waters of Post-Glacial Time, to which environment its peculiar form 
is undoubtedly due. As remarked by Dr. Dall, the recent shells are 
less variable, on the average, than are the fossil forms. Galbana will 
probably be found to be one of our commonest species when it becomes 
fully recognized ; in many cabinets it now reposes, without doubt, under 
the names of desidiosa and humilis. I cannot agree with Dr. Dall 
(op. cit., p. 74) in making traski Tryon a synonym of galbana. It 
scems to me to be related to proxima. Its size of 16 mill. is far greater 
than any galbana I have seen, and its shape, as figured and described - 
by Tryon and as shown by his type, is totally different. 
Galba petoskeyensis (Walker). Plate XXVI, figures 14-16. 
Lymnea petoskeyensis WALKER, Nautilus, XXII, p. 6, pl. i, figs. 3, 5-7, May, 
1908. 
SueLL: Elongated, compressed, thin; periostracum light yellow- 
ish horn; the shell is almost white and translucent; surface shining, 
growth lines prominent, crossed by impressed spiral lines, giving the 
surface the wavy appearance of the typical Lymneas ; the last whorl 
is sometimes malleated; whorls 6-614, rather flat,sided, shouldered at 
the periphery on the spire whorls, the last whorl somewhat roundly 
compressed; nucleus very small, rounded; hyaline; the first whorl is 
very minute, the second is very large (pl. XLIX, fig. G) ; spire acutely 
conical, generally a trifle longer than the aperture; sutures well im- 
pressed; aperture an elongated oval, rounded and somewhat effuse 
anteriorly ; the posterior portion of the aperture forms an acute angle ; 
outer lip thin, with a white internal thickening or varix within the 
edge; inner lip broadly reflected, flattened and emarginating the con- 
spicuously open umbilicus ; parietal callus rather thick; at the junction 
of the inner lip with the parietal wall, the former is abruptly pressed 
