OF NORTH AMERICA. 283 



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 peninsula 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 XXXI.) 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 falustris. 



Galba obrussa peninsulas (Walker). Plate XXXII, figures 1-G. 



Limncca desidiosa RUTHVEN, Rep. Mich. Acad. Sci., VI, p. 190, 1904. 

 WALKER and RUTHVEN, Rep. Geol. Surv. Mich., 1905, p. 95, 1906. 



Lymnaa desidiosa var. peninsula WALKER, Nautilus, XXII, p. 9, 163, pi. 

 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. 



