198 THE CHICAGO ACADEMY OF SCIENCES. 



reeds, but never more than four inches from the base, while A. paral- 

 lelus, though rather scare, is found from ten to eighteen inches above 

 base. 



"Unlike other Lymnseas, gracilis attaches itself very firmly to its 

 resting place. Unless a gentle, sliding movement is made in removing 

 it, the delicate lip is apt to become broken in the operation. If traction 

 is made along the long axis of the shell, the empty shell will be found 

 between thumb and finger, the animal clinging to the reed having suf- 

 fered a rupture of its attaching muscle to occur rather than relax its 

 hold" (Kirkland). 



''After finding dead specimens of this beautiful species in Belle 

 Lake, I was told by Prof. Hubbard that he took it alive in Heath Lake 

 in the previous fall, upon the under side of lily leaves. Later a thor- 

 ough search was made for them in the same locality, but only two 

 dead specimens were found. Query, where do they keep themselves 

 in summer?" (Sargent, Minnesota habitat.) 



In captivity the animal moves about slowly in the aquarium and 

 will also rest for hours with half its shell out of the water, the animal 

 being attached to the glass side of the aquarium. 



REMARKS: Haldemani is the slenderest of our Lymnseas, its 

 height beng five times its breadth. It is also very thin and fragile. It 

 cannot be mistaken for any other species, its graceful, oblique whorls 

 and slender form at once distinguishing it. From the reports of those 

 who have collected this species it would seem to inhabit the deeper 

 water generally, coming toward the shore at different seasons. It is 

 very common in some localities and rather rare in others. The Lake 

 Champlain specimens average rather smaller than the western forms. 



The very appropriate name of gracilis is preoccupied by Ziethen, 

 and in 1867 Binney used the name haldemani, as suggested by Des- 

 hayes. 



Genus PLEUROLIMNJEA Meek, 1866. 



1866. Pleurolimnaa MEEK, Check List N. Amer. Fos. Eocene, pp. 9, 34 (type, 



Limn&a tenuicostata Meek and Hayden, Eocene). 



1870. Pleurolimnaa BALL, Ann. Lye. Nat. Hist. N. Y., IX, p. 349. 



1876. Pleurolimncea MEEK, Rep. U. S. Geol. Surv. Terr., IX, p. 533. 



1883. Pleurolimnaa FISCHER, Man. Conch., p. 506. 



1884. Pleurolimncea TRYON, S. and S. Conchology, III, p. 101. 

 1905. Pleurolimnaa DALL, Alaska Mollusks, p. 64. 



1908. Pleurolimneea BAKER, Science, N. S., XXVII, p. 943. 



RANGE: Eocene period. 



SHELL: "Differing from the last (Acella) in having small, regu- 

 lar surface-costse parallel with the lines of growth, the aperture nar- 

 rowed or siibangular, instead of rounded anteriorly" (Meek). 



