5 

 Aplexa, Aplexus, and lastly Aplexia. 



36 Planorbis canipanulatus 



Hartland, Vermont, rare. 



37 Planorbis bicarinatus 



Abundant, Hartland, Vermont. 



38 Planorbis exacutus 



Rare, Hartland, Vermont. 



39 Planorbis Lentus 



Rare, Hartland, Vermont. 



40 Planorbis parvus 



Diameter 5 mm; shell compressed, minutely striate, smooth, 

 flat above, with center impressed; left side with a broad, shallow 

 concavity; whorls 4, a great part of them, with the apex visible to 

 the center, on both sides; sutures equally deep; aperture oval, 

 oblique, longer than wide, peritreme undeviating; color light 

 brown, sometimes with a greenish tinge. 



Hartland, Vermont, rare. Cantilles canyon, Baja California, 

 on Chara, and other aquatic plants, abundant. Widely distrib- 

 uted. 



41 Limnaea palustris 



Shell of moderate size, spire well elevated, whorls moderately 

 inflated, subperforate, aperture somewhat narrowly auriculiform, 

 columellar fold well developed; color variable from light to dark 

 brown. 



Hartland, Vermont, common; Tracy cites a black form as rare. 

 Widely distributed. 



42 Limnaea desidiosa 



Hartland, Vermont, rare. West to Kansas. 



43 Limnaea caperata 



Shell suboval, a little oblong, obscurely yellowish horn color; 

 spire half as long as mouth; apex acute; whorls slightly wrinkled 

 across, and with very numerous, equal, subequidistant, elevated, 

 minute, revolving lines; suture not very deeply impressed; aper- 

 ture rather dilated; lip fold not profound. 



Hartland, Vermont, rare. Hudson's bay, south to New York; 

 Michigan; Idaho; Utah. 



44 Ancylus parallelus 



Hartland, Vermont, rare. 



45 Valvata tricarinata 



Abundant in the Connecticut river, Hartland, Vermont. Wis- 

 consin. 



46 Melantho decisa 



Windsor Co., Vermont, common. 



47 Amnicola limosa Say 



Hartland, Vermont, abundant. Utah. 



48 Carychium exigunm 



Oval-elongate, white, translucent, shining; spire long, apex 



