^°l89a"'] PROCEEDINGS OF THE NATIONAL MUSEUM. 207 



Helix (Arionta) magdalenensis sp. nov. 



Plate XV, Figs. 11, 12, 13. 



Shell orbicular, much depressed, apex whorls but very slightly 

 elevated, suture well detiued. Whorls three aud a half to lour, flattened 

 above, slightly obtusely augulated on the periphery, and rounded 

 below. Umbilicus open, showing the whorls ; upper line of the mouth 

 more or less slanted downward where it joins the body whorl, varying 

 in this character in different specimens. Aperture broader than high, 

 ovate, somewhat oblique, slightly eifuse, and thickened and reflected a 

 little at the edge, more so in the umbilical region, where it partially 

 overhangs the umbilicus. In some examples a thin deposit of callus on 

 the parietal wall suggests a continuous peristome. Surface sculptured 

 by the ordinary lines of growth, which vary in prominence in different 

 individuals. Color, dingy whitish, the specimens, nine in number, being 

 dead, with an obscure, narrow, reddish-brown band just above the 

 periphery. 



Dimensions. 



Millimeters. 



Maximum diameter of largest 13 



Minimum diameter of largest 10 



Altitude of largest 6. 50 



Maximum diameter of smallest 10. 50 



Minimum diameter of smallest 9 



Altitude of smallest _ 5. .50 



Habitat. — Magdalena, State of Sonora, Mexico, on the line of the 

 Sonora, New Mexico aud Arizona Eailroad, which termiuates on the 

 Gulf of California at Guaymas. It was detected by Mr. V. Bailey 

 among rocks on the top of a mountain at an elevation of 1,000 feet above 

 the town. (U: S. National Museum, No. 104094.) 



This species in its principal features, indicates a relationship with its 

 geographical congener, H. Botcelli, Newcomb, which has been found in 

 the Salt River Mountains, 7 miles north of Phoenix, Arizona (Pilsbry). 

 H. Lohri Gabb, which is regarded as a synonym of Boivelli, collected by 

 its author on the table-lauds of Lower California near Mulege, and it 

 has also been credited to Chihuahua, Mexico, and farther eastward to 

 " Texas," upon what authority I am not aware. The relationship of 

 H. magdalenensis to Rowelli is like that of the Califoruian snails H. exa- 

 ata to H. arrosa, of the small forms of R. fidelis to H. mormomim, or 

 of E. Stearnsiana to H. Kellettii, etc. Its dimensions are in every way 

 less than those of Rowelli+ Lohri. 



The helicoid forms described herein belong to the Arionta group, and 

 may be regarded as the southern geographical aspect or an extreme or 

 extra-limital expression thereof. 1 agree in the main if not altogether 

 with Mr. Pilsbry in his remarks as contained in the paragraph uuder 

 the head Lysinoe in the Proceedings Academy Natural Sciences of Phil- 

 adelphia, 1889, page 193,* criticising the generic terras, etc., heretofore 

 * Nomenclature and check-list of N. A. laud shells. 



