164 PROCEEDINGS OF THE ACADEMY OF [March, 
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. b. 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. techella was formerly con- 
sidered by one of us to be a synonym or race of L. cubensis Pfr., and 
L. bulimoides 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 Lymnea 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 carus n.sp. Pl. IX, figs. 4, 5. 
Shell discoidal, biconcave, the spiral on the left side slightly more 
sunken and narrower than on the right. Whorls 34, 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 strive separated by slightly narrower deep grooves. Pale 
brown incolor. 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 débris. 
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 
