1915.] NATURAL SCIENCES OF PHILADELPHIA. 401 



river valley, and will eventually be found again. Great quantities 

 of the drift debris of the Santa Cruz which we looked over did not 

 produce a second specimen, though minute shells were abundant. 

 Only by a rare chance would so turbulent a stream as the Santa Cruz . 

 in flood carry Sonorella very far. In its ordinary condition there is a 

 succession of small pools connected, in places, by a slender rivulet; 

 but after heavy rain we have seen turl^id water from bank to bank 

 for a brief time. 



Sonorella tumamocensis n. sp. P!. X, figs. 4, 4a, 46. 



The shell is depressed, umbilicate (umbilicus contained about 

 6 times in the diameter of the shell), thin, light pinkish cinnamon, 

 fading to whitish on the base, and having indistinct whitish borders 

 above and below the rather narrow chestnut-brown shoulder band. 

 Apical sculpture is of the hachitcma type, but usually very Vv^eak, the 

 initial half-whorl smooth, without the usual radial ripples; the 

 rest of the embryonic shell is marked with a few delicate, interrupted 

 tangential (protractive) threads, on a nearly smooth ground, having 

 weak growth ripples only. The subsequent neanic and last whorls 

 have weak growth lines. Whorls 4^, convex, the last slowly de- 

 scending in front. Aperture rounded, nearly as high as wide. Peri- 

 stome thin, the outer and basal margins very narrowly expanded. 

 The columellar lip, in basal view, shows very little dilation. 



Alt. 10.5, diam. 17.5 mm.; aperture 8.7 x 9.5 mm.; umbilicus 

 2.8 mm. wide. 



Other specimens measure: 



Alt. 10.5, diam. 18 mm. 

 " 9 " 17 " 

 '' 9^ " 16 " 



Genitalia (PI. XIII, fig. 5). — The penis is about as long as the 

 vagina, slender in its lower part, somewhat swollen above. Around 

 the base there is a very short sheath of very loose open texture. It 

 contains a slender, slowly tapering papilla about one-third as long as 

 the penis, its surface closely grooved spirally, the apex obtuse but 

 small. The epiphallus is slender, terminating in a vestigeal, bud- 

 like flagellum. The retractor muscle is inserted on the epiphallus. 

 Other organs as usual. 



Top of the head and back are slate-colored, shading into gray 

 on the sides, whitish towards the edges of the foot. Tail and sole 

 white. Faint lines define the three areas of the sole. Jaw (PI. 

 XIII, fig. 8) has 3 or 4 very weak ribs. 

 26 



