148 NIK CHICAGO ACADEMY OF SCIENCES. 



and measured as follows: Length, 54.00; breadth. 30.50; aperture 

 length, 39.50; breadth, 16.00 mill. (No. 70370;. The progeny at eight 

 months were very narrow, quite unlike the parent shell. 



An albino stagnalis is reported by Mr. F. R. Latchford from Chil- 

 cotts' Lake, Masham, Ontario, in the Ottawa Naturalist, VI, p. 118. 

 The shell is described as being as "white as pearl." Albinism in this 

 species is also reported by several European authors. 



Lymncea stagnalis is the host of several species of cercariae (larva; 

 of trematode worms) which infest the pulmonary cavity. They seem 

 to occasion no especial inconvenience to the animal. 3 



Remarks : A thorough revision and a careful study of a large 

 collection of American stagnalis has made it evident that Say's jugularis 

 (as defined by Haldeman and Binney) cannot be separated from 

 appressa when large numbers of individuals are examined from various 

 localities. When compared singly such forms as figure 9, plate XIX, 

 seem quite distinct from jugularis as shown in figure 6, but when 

 several hundred specimens are examined from the same locality these 

 differences disappear and no line can be drawn between them. Both 

 forms occur in the same geographic area and are almost always found 

 associated together. They offer no anatomical differences. Say's types 

 of appressa closely resemble Binney's figure 28, and this form must 

 be taken as the type of the race appressa. Haldeman's figured speci- 

 mens of both appressa and jugularis are faithfully portrayed on his 

 plates 4 and 5. A specimen of his jugularis measures as follows : 



Length, 44.00; breadth, 21.00; aperture length, 25.50; breadth, 

 12.00 mill. 



It is unfortunate that Say's types of jugularis cannot be found. 

 The name was doubtless founded on immature material, as the size 

 given by Say is but one inch. Immature individuals of appressa of 

 5^2 or 6 whorls measure about an inch and correspond in every way 

 with Say's description. Say's reference to a specimen from the West 

 Indies is, of course, quite erroneous ; the only Lymnsea from this region 

 resembling stagnalis is Pscudosuccinea francisca, from Cuba, which 

 is much smaller and of a different shape. 



Stagnalis appressa is a characteristic Lymncea, easily known wher- 

 ever found. It differs from typical stagnalis principally in its more 

 graceful, fusiform shape. The aperture is more oval and not so angular 

 and the columellar callus is more closely appressed to the parietal wall, 

 giving the axis a conspicuous twist which is absent in most specimens 



3 See Hogg, Trans. Roy. Micr. Sec. Ill, p. 232, 1870 for description of Cer- 

 caria furcata. 



