THE NAUTILUS. & 



Orizosoma, new subgenus of Streptostyla. 



Shell perforated, the columella thickened, simply concave, almost 

 imperceptibly sinuous above. 

 Streptostyla (Orizosoma) tabiensis, n. s|.. 



Shell ovate- turreted, rather thin, smooth, the base deeply indented 

 and minutely umbilicated; whorls 6, the three earlier distorted ;. 

 aperture narrow, 5 the length of the shell, outer lip sinuons; colu- 

 mella thickened, concave. Alt. 9'8, diam. 4*8 mill. 



Cave at Tabi, Yucatan. 



Carychium exiguum mexicanum, n. \;\r. 



Shell cylindrical ; whorls 4^ ; aperture equalling or a trifle ex- 

 ceeding I of the total length. Outer lip thickened at and below the 

 middle by a very heavy deposit of callus upon its face; columellar 

 fold subobsolete. Surface delicately striated. Alt. 1'8, diam. 'S mill. 



Orizaba, Mexico. 



Physa osculans var. Patzcuarensis, n. var. 



Shell thin, obconic, broad abov^, narrow below ; spire small, 

 acute, whorls 4, rapidly enlarging ; columella long, vertical, slightly 

 sinuous ; color light brown or whitish. No internal lip-rib ; surface 

 smooth. Alt. 15, diam. 11 mill. 



Lake Patzcuaro, Mexico. 



Holds the same relation to Ph. osculans Hald. that ancillaria -|- 

 Parkeri hold toward Ph. heterodropha. The rationale of these 

 bulging, broad-topped forms of Physa is discussed in my paper in 

 Proc. A. N. S. Phila. 

 Potamopyrgus ? Bakeri, n. sp. 



Shell slender, elongated, composed of Oa very convex whorls; 

 aperture ovate, its length contained more than three times in the 

 length of the shell. Surface marked by delicate growth-lines, hav- 

 ing low, inconspicuous longitudinal folds, sometimes quite regular 

 and well marked on the upper whorls, and encircled by numerous 

 fine, subobsolete spiral strise. Alt. 4, diam. r9 mill. 



Yautepec, Mexico. 



Has much the genei'al aspect of Tryonia protea Gld. It is named 

 in honor of Mr. Frank C. Baker who collected the specimens. 

 Pyrgulopsis ? Patzcuarensis, n. sp. 



In general form like P. nevadensis Stearns. Whorls acutely 

 keeled in the middle, convex above the keel, the last whorl obtusely 



