98 THE NAUTILUS. 



Vivtparus. This character serves to differentiate it from Paludes- 

 trina, which the smooth phase resembles in shell structure. 



Amnicola crosseana n. sp. PI. ix, fig. 6. 



The shell is perforate, ovate-conic, corneous, smooth, the growth- 

 lines being scarcely visible. Whorls 5, the first very minute, the 

 rest not very convex; suture but slightly impressed, having a gray 

 border (by transparence) below. Umbilical region defined by an 

 angle. Aperture ovate, slightly oblique. Peristome thin, narrowly 

 olive-edged, represented by an adnate transparent callus on the 

 parietal wall, which is rather long. 



Length 3.1, diam. 2, length of aperture 1.6, width 1.1 mm. 



Found only in ponds at La Barra, near Tampico. 



This species was taken in considerable numbers. It has some 

 resemblance to A. gnatemalensis Crosse & Fischer {Pahidina hyalina 

 Morelet, not Anton), but on comparing a specimen received from 

 Morelet it is noticed that guatemulensis has much more convex 

 whorls and a shorter more rotund aperture. A guatemalensis is very 

 closely related to A. panamensis Tryon. I doubt whether the two 

 forms are specifically distinct. 



A. crosseana, named for M. Hippolyte Crosse, is distinct from 

 species of the Texan region by its lengthened shape, rather pointed 

 apex, the weak convexity of the whorls, the long adnate parietal 

 callus and the angulation around the umbilical region. With the 

 milky corneous examples there are many of a brown or russet tint, 

 probably owing to a thin ferrous incrustation. 



Amnicola comalensis Pils. & Ferr. from Texas described in the 

 Proc. Acad. Nat. Sci., Pliila., 1906, p. 171, fig. 37, is a much 

 stouter shell than A. crosseana. In the description the length was 

 given by error as 3.9 mm. It should have been 2.9 mm. 



SOMATOGYRUS MEXICANUS n. Sp. PI. ix, fig. 3. 



The shell is perforate, globose, higher than wide, corneous, 

 smooth, solid but rather thin. Whorls 4|^, strongly convex, parted 

 by a deep suture, rather slowly increasing at first, but at the last 

 whorl very rapidly enlarging. The last whorl is very convex, and 

 descends more rapidly near the aperture. The aperture is ovate, 

 subangular above. The outer lip is a little curved forward in the 

 middle, or in other words, retracted above, thin-edged. The inner 



