164 PROCEEDINGS OF THE ACADEMY OF [Marcll, 



The young of one season have a comparatively shorter spire than 

 old shells, the rate of descent of the suture progressively increasing 

 somewhat. As usual, there are only traces of malleation at this stage. 

 The erosion of the apices in all but one of the type lot (as mentioned 

 by Haldeman) makes them shorter than they would otherwise be, 

 giving much the appearance of L. h. cockerelli. Abundant series from 

 Houston and San Marcos collected by Pilsbry, with others from various 

 naturalists, demonstrate the identity of Haldeman's shells with the 

 larger-spired adult form figured above. L. tecJiella was formerly con- 

 sidered by one of us to be a synonym or race of L. cubensis Pfr., and 

 L. hulimoides was treated as a variety of the same species. They are cer- 

 tainly very similar, but cubensis has a more triangular and less broadly 

 developed columellar expansion; and in view of the way Lymnoea is 

 being split up into species and races, it may be best to retain the several 

 forms as distinct species or races until the subject can be taken up with 

 ample material and time for the study of Antillean and Mexican forms 

 together with our own. 



Planorbis trivolvis Say. 



Specimens referable to typical P. trivolvis were taken in Comal county, 

 and at Del Rio, Devil's river and the Pecos river, Val Verde county, 

 Texas. 



Planorbis bicarinatus Say. 



Guadalupe river, Comal county, Texas; abundant and typical. 

 Planorbis cams n. sp. PI. IX, figs. 4, 5. 



Shell discoidal, biconcave, the spiral on the left side slightly more 

 sunken and narrower than on the right. Whorls 3^, convex, the last 

 round peripherally and on both -sides, curving more abruptly into the 

 concavity on the left side. Sculpture of close, very regular obliquely 

 radial rounded striije separated by slightly narrower deep grooves. Pale 

 brown in color. Aperture but slightly oblique, heart-shaped, peristome 

 thin, acute, a trifle dilated at its insertions. Diam. 3.3, alt. (thickness) 

 1 mm. 



"Sinking Spring" near San Marcos, Hays county, Texas; Guada- 

 lupe river about four miles above New Braunfels, Comal county. Rio 

 San Filipe and Devil's river, and canyon of the Pecos river about a mile 

 above the High Bridge, Val Verde county; everywhere in drift debris. 

 Types from the last locality. 



This little Planorbis is very distinct by its beautiful sculpture, con- 

 stant in numerous specimens from five rivers in central and western 

 Texas. It is much more abundant in the Rio Grande drainage than 



