THE NAUTILUS. 79 



Physa mexicana Phil. Tampico and Valles. Young shells were 

 numerous in some of the shallow pools, the larger ones being rather 

 scarce. 



Physa osculans Hald., var. rhyssa Pils. Roadside pool near 

 Valles with Lym. cubensis, the only place these two species were 

 found. Differs from P. mexicana in having a more attenuate spire, 

 one more whorl, and the body whorl is less inflated. 



Physa sp. This is thicker than the P. mexicana and has the 

 chestnut-colored callus within the outer lip, which in the larger 

 examples shows at previous stages of growth. 



Ancylus excentricus Morelet. Found on plants in Tamesi and 

 Valles rivers ; scarce ; a fragile species. 



VALVATID^E. 



Valvata humeralis Say. Valles river. 



AMNICOLIDJE. 



Cochliopa riograndensis Pils. & Ferr. Valles river. More ele- 

 vated than Valvata humeralis and differs from it in having several 

 colored spiral lines, giving it a striking resemblance to a small Helix. 

 The operculum and teeth, examined by Dr. Pilsbry, show it to be 

 correctly referred to Cochliopa. The aperture is angular above, thus 

 differing from that of Valvata. 



Amnicola guatemalensis C. & F. Tampico, on pieces of wood in 

 ponds. 



Amnicola tryoni Pilsbry. Tampico, drift ; a smaller species than 

 guatemalensis. 



Potamopyrgus coronatus Pfr. Tamesi river, Tampico. The 

 spines on the shoulder are well developed for so small a species. 



Potamopyrgus coronatus texanus Pils. Valles river, only two 

 examples secured, they do not show the spines. 



Paludestrina tampicoensis Pils. & Hinkl. Tampico. 



MELANIIDJS. 



Pachycheilus vallesi Hinkley. Plentiful in the Valles river. 



UNIONID^E. 



Unio tampicoensis Lea. Valles river. 



Unio popei Lea. Valles river. Pilsbry says of these shells " I 

 think they are correctly referred to popei Lea, as a variety. It 

 differs from typical Texan popei in the dark nacre and the more dis- 

 tinct green rays. It is related also to U. soledadensis Crosse & 



