OF NORTH AMERICA. 267 



it joins the parietal wall is somewhat abruptly curved in. The colu- 

 mella is also straighter than in humilis. These distinctions hold good 

 in the presence of the rather large series of humilis examined. Some 

 specimens of modicclla, however, closely approach humilis, especially 

 in. the form of the inner lip, which sometimes wholly lacks the peculiar 

 compression at its junction with the parietal wall. (See plate XXIX, 

 fig. 35; pi. XXXI, fig. 4.) The South Carolina specimens of humilis 

 also vary in this respect. (Compare the figures on plate XXIX.) The 

 rounder aperture, more obese body whorl and broadly conic spire of 

 humilis appear, however, to be constant. Modicella may be distin- 

 guished as a race occupying the whole of the United States except 

 the southeastern states bordering the Atlantic Ocean and the Gulf of 

 Mexico. Some forms of Galba bulimoides cassi somewhat resemble 

 modicella, but may be distinguished by the form of the inner lip. 

 Parva and sterkii also differ in the form of the inner lip. Obrussa 

 has a differently shaped aperture and the inner lip is notably com- 

 pressed and bent inward at its junction with the parietal wall. G alb ana 

 is similar in some of its forms, but is typically shorter, more corpulent 

 and with a more depressed spire, more shouldered whorls and a rounder 

 aperture. Young specimens of Galba bulimoides from California 

 have been mistaken for modicella. A form of modicella occurs 

 at La Porte, Indiana, which has a strongly zebra-marked shell, the 

 narrow white stripes standing out vividly against the dark brown back- 

 ground. As many as fourteen stripes may be counted on the last whorl 

 of one specimen. 



The spire in modicella varies greatly in length, the short-spired 

 individuals being the form commonly known as humilis. No line can 

 l)e drawn between the short and long-spired specimens, as every kind 

 of intermediate form occurs. (See the figures on plate XXIX.) From 

 the records it would appear that Say at first considered the narrower 

 form the same as his humilis, for he says in his description : "A va- 

 riety of it, sometimes quite black, was found by Dr. McEwen, at 

 Owego, on the Susquehanna." Under modicella he writes: "It was 

 found by Dr. McEwen at Owego, on the Susquehanna River, near 

 the state of New York." There is no question, I think, but that modi- 

 cclla was founded on the same specimens spoken of under humilis, 

 and it also seems evident that Say considered them distinct from his 

 North Carolina humilis. The types of modicella are preserved in the 

 Philadelphia Academy and conform closely to Binney's figure and to 

 the shells figured on plates XXIX and XXXI of this monograph. 



Lea's jamesii (pi. XXXI, fig. 1), of which the cotype is in the 



