172 PROCEEDINGS OF THE ACADEMY OF [March, 
other species being Central American. The shell has much the ap- 
pearance of Valvata, but is readily distinguished from that by its ovate, 
not circular aperture, which is more or less conspicuously angular 
above, and by having the whorls more compactly coiled. It should, 
however, be said that we could not verify the generic reference of C. 
riograndensis by examination of the operculum or radula, as unfor- 
tunately none of the shells we obtained were living, though some were 
fresh in appearance, and the operculum was not found. It consists of 
few whorls in Cochliopa, as in Amnicola, while that of Valvata is 
many-whorled with central nucleus. 
C. riograndensis is not closely related to any of the known species, 
being of lighter texture, much more openly umbilicate, and with some- 
what different sculpture. 
VALVATIDA. 
Valvata micra n.sp. Pl. IX, figs. 7, 8, 9. 
Shell excessively small, composed of 24 tubular whorls; spire nearly 
flat; the last whorl is nearly round, barely or not quite in contact 
with the preceding at the aperture, near which it enlarges more rapidly. 
Suture deep. Surface finely, weakly striate. Aperture moderately 
oblique, subcircular, the peristome simple, continuous. Umbilicus 
ample but rapidly narrowing within. 
Alt. .48, diam. 1.15 to 1.2 mm. 
Drift débris of Guadalupe river about four miles above New Braun- 
fels, collected by Pilsbry and Ferriss, 1903. 
This is one of the smallest mollusks known, yet the dilation of the 
“ Prof. von Martens defines four species of Cochliopa in the Biologia Centrali 
A mericana—guatemalensis Morel., tryoniana Pils., trochulus and infundibulum 
Marts. (pp. 428, 429). He omits C. rowelli Tryon, which was originally described 
from Clear Lake, California. Rev. J. Rowell, who found the original specimens, 
now states (in litt.) that ‘‘Cochlicopa Rowellii was named from shells collected 
by me near Baulinas Bay (not Clear Lake), Marin county, California.’’? There 
are authentic specimens from Central America in the collection of the Academy, 
ae that I still doubt whether the species really was actually collected in Cali- 
ornia. 
Prof. von Martens surmises that C. guatemalensis (Morel.), which he had 
not seen, may not be different specifically from C. tryoniana; but it is in fact not 
even closely related to that species, being very much smaller, more depressed, 
and evenly sculptured with threadlike spirals. The suture descends shortly in 
front in fully mature shells. An additional locality is Polvon, in western Nicara- 
gua (MeNiel in coll. A. N.S. Phila.). I have examined the radula of C. guate- 
malensis which proves to be Amnicoloid, and demonstrates the species to be a 
Cochliopa, not a Valvata as Morelet supposed. The central tooth has the formula 
4.14 
3-3» the inner lateral has 6 denticles, the third from the inside being largest, 
and its body has the usual boss or projection below. The inner uncinus has 13, 
the outer very many excessively minute denticles. 
