266 PROCEEDINGS OF THE ACADEMY OF [1893. 



the plate of attachment. A radula was 0*58 mm. long, 0*2 wide, 

 thus one transverse row measures about 0*009 mm. in length. 



The ganglia are described above. 



This is a North American species, occurring apparently almost 

 exclusively in the prairie States. I have seen specimens from Joliet 

 and Ottawa, Illinois ; Davenport and Bonair, Iowa ; numerous 

 examples in drift on the Missouri River, collected at Eastport, 

 Iowa, together with V. costata and a few perspectiva; Nebraska; 

 Wichita, Kansas; Indian Territory. Doubtless many of them are 

 in collections under the name costata, etc. 



V. parvula much resembles costata, but it is decidedly and con- 

 stantly smaller, having scarcely half the bulk of the latter, and dis- 

 tinguished by the comparatively wider umbilicus and by the last 

 whorl not descending, the peristome, as a rule, being quite straight 

 on the back to margin, as shown in Man. Conch., PI. 32, fig. 25. 

 Sometimes it is gradually and slightly ascending, as in V. costata, 

 pulchella, excentrica. Never have I seen a doubtful specimen 

 between parvula and costata, and they inhabit the same region. 

 Our species also resemble perspectiva in color, size and presence of 

 the ribs ; the differences will be pointed out in connection with the 

 latter species. 



V. parvula shows a little variation. The average size is scarcely 

 2"0 mm. ; one is found with 2*1, but some are as small as 1*7. The 

 lip is almost always comparatively strong, and the aperture always 

 rather circular, sometimes as shown in fig. 26. One specimen 

 from Bird's Bridge, Will County, Illinois, among about eight which 

 I owe to the kindness of Mr. Ferriss, has the last whorl descending, 

 the peristome continuous and free from the penultimate, thus resem- 

 bling V. perspectiva ; but the strong lip and the rather circular, not 

 transversely elongate aperture characterize it as parvula. The 

 abnormity may be caused by a breakage, as in other species. 



For a time I regarded this Vallonia. as americana of Ancey (ms.) 

 Mr. Theo. D. A. Cockerell kindly furnished me a copy of Ancey's 

 ms. description which I communicate here : V. americana differs 

 from cyclophorella by its " taille plus faible, son ombilic tres-grand 

 aussi [?] et fortement dilate au dernier tour, ses tours a croissance 

 plus rapide, et en nombre moindre (31 seulement) son dernier tour 

 nullement descendant, plus ample a sa terminaison, son peristome 

 fortement epaissi, son ouverture a bords distants et beaucoup plus 

 grand," etc. From costata it differs " par l'ampleur de sou dernier 



