Mollusca 139 



only an abnormal form of P. trivolvis. Henderson suggests that 

 the snails may have been affected by a parasite, but this is subject 

 to confirmation. Similar abnormalities are known in other species 

 of Planorbis. I have seen a specimen of the fossil P. euomphalus 

 of Sowerby, from Tertiary beds at Headon Hill, Isle of Wight, in 

 which the coiling is so irregular that one might be at a loss to 

 guess the genus of the shell. Yet, strangely enough, irregularities in 

 coiling are not necessarily abnormal, in snails. A most extraor- 

 dinary case is that of the little land snail Protoboysia, fossil in the 

 Eocene strata in Clark's Fork Basin, Wyoming. The shell has 

 a broadly conoid form, with many whorls, but the last whorl is 

 abruptly directed upward, obliquely wrapping the spire, curving 

 round it near the apex. This is the regular structure of the genus, 

 all the individuals being the same. Although the Protoboysia 

 has only been found in Wyoming, it doubtless also inhabited what 

 is now Colorado. 



The species of Lymnaea are rather numerous, some of them 

 large and handsome shells. Very big ones with a long tapering 

 spire are L. stagnalis, a species very common in Europe as well as 

 America. The American forms are usually referred to the sub- 

 species called appressa of Say, and this includes apparently all 

 the Colorado shells. A shell with a very wide aperture and 

 expanded lip, but the spire short and sharp, is the L. auricularia 

 of Linnaeus, the name referring to the resemblance to the human 

 ear. This is not a native of Colorado but of Europe; it has been 

 found, accidently introduced in some way, at Colorado Springs 

 and near Fowler. Although Lymnaea is a genus of aquatic snails, 

 some of the species can survive for a considerable time out of 

 water. The broad rounded L. bulimoides subspecies cocker elli of 

 Pilsbry and Ferriss is found in pools near the foothills in Montana, 

 Colorado, New Mexico, etc. These pools dry up, and the snails, 

 as well as certain Crustacea, survive in the mud, ready to resume 

 activity whenever the rains come. Pilsbry had some of these 

 snails packed in cotton for 45 days, but on putting them in the 

 water they cheerfully crawled about, and even when supplied 

 with water were often seen leaving it and crawling to the top of 

 the glass in which they were confined. On one occasion I found 

 a number of small Lymnaea snails on the outside of flower pots 

 in a greenhouse at Boulder, Colorado. They were on a moist 



