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LYMNAZIDA OF NORTH AMERICA. 28 
A peculiar form of obrussa occurs at La Porte, Indiana (in Clear 
Lake), which when half grown has the general form of Galba humilis 
modicella and the spire has the rounded whorls of Galba obrussa plica. 
(Pl. XXXI, figs. 35-37.) The adult shells, however, are typical obrussa. 
This fact illustrates the supreme importance and value of studying a 
large series from each locality. At Lebanon, Pennsylvania, a form 
occurs with a very acute spire and a much expanded aperture, resem- 
bling in outline Galba davisi (Walker). (See plate XXVI, figures 
11-13.) This form approaches Galba obrussa peninsule in the acute- 
ness of the spire, but the body whorl is quite convex. A somewhat 
similar form occurs in Monocacy Creek, Bethlehem, Pennsylvania, 
differing in the aperture, which is purely of the obrussa type. (Figs. 
8-10.) These variations are not stable and are all sports or mutations. 
Haldeman’s figures on plate 10 of his monograph are all founded- 
on true obrussa, although figure 7 is abnormal. The specimens are 
preserved in the Philadelphia Academy, No. 58702. Figure 14 repre- 
sents the acuta of Lea. All of the forms figured on Haldeman’s plate 
have been collected by the writer, excepting the one represented by 
figure 7, which is probably unique. (Compare Haldeman’s figures 
with those on plate XX XI.) Binney’s figure 68 is questionable, though 
it may represent an elongated form of obrussa. 
This species has long been known under the name of desidiosa, 
but that name should be applied to a totally different species, a fact 
made clear by an examination of autotypes in the Philadelphia Acad- 
emy. See under palustris. 
Galba obrussa peninsule (Walker). Plate XXXII, figures 1-0. 
Limnea desidiosa RuTHVEN, Rep. Mich. Acad. Sci., VI, p. 190, 1904.— 
WALKER and RuTHVEN, Rep. Geol. Surv. Mich., 1905, p. 95, 1906. 
Lymnea desidiosa var. peninsule WAKER, Nautilus, XXII, p. 9, 163, pl. 
ii, fig. 7, May, 1908. ; 
SHELL: Of good size, slender, elongated ; periostracum yellowish 
or brownish horn; surface dull to shining, growth lines rather coarse 
and heavy, spiral lines faintly impressed on some specimens, very 
heavily impressed on others; whorls 6, very convex, body whorl sub- 
cylindrical, somewhat compressed; spire long and acute, subturreted 
to turreted; sutures deeply impressed; aperture oval, not notably ex- 
panded; outer lip thin; inner lip narrowly reflected, forming a tri- 
angular expansion, narrow and erect at the lower part of the aperture, 
wide and flatly appressed to the parietal wall at the upper part; um- 
bilical chink very narrow. 
