17 1 III; ADEMY OF SCIEN 



Geological Range: Pleistocene. Loess. Otis Mill. Union 

 County, South Dakota i Smith Coll. ). 



Ecology : Probably the same as for typical columella ; mud pool 

 in old lime quarry i Lermond, Main 



Remarks: Chalybca is distinguished by its narrow shell, com- 

 pressed acuminate spire, flattened body whorl and narrow and very 

 effuse aperture. The excavated and arched columella is peculiar and 

 will easily distinguish this variety from any form of typical columella. 

 The spire is compressed and the aperture varies from elongate-ovate 

 to expanded or even flaring. The columellar plait is very pronounced 

 in this variety. The names included in the synonyms all seem minor 

 variations of one form, although coarctata seems to stand midway be- 

 tween chalybca and casta. Its peculiar columella seems to ally it rather 

 with chalybca. Chalybca is not as narrow as casta, from which it is 

 also distinguished by its deeply excavated and strongly arched colu- 

 mella. In some localities the variety- chalybca takes the place of typical 

 columella. 



Pseudosuccinea columella casta Lea . Plate XXIV, figures 

 14-19. 



Lytnnea casta Lea. Proc. Arner. Phil. Soc, II, p. 33. 1841; Trans. Amer. 

 Phil. Soc... IX.. pp. 10. 11. 1844; Obs.. IV. pp. 10. 11. 1848. 



Lymnoea casta Wheatley, Cat. U. S. Shells, p. 23, 1845. — Morse.. Amer. 

 Xat., Ill, pi. 11, fig. 15, 1870.— Scudder, Bull. Nat. M115., 23, pp. 33, 43, 200, 1885. 



Limncea casta Bixxey, Check List, p. 12, 1860; Land & F. W. Sh. X. A.. II. 

 p. 26. fig. 43, 1865.— Tsyon, Con. Hald. Mon., p. 89 (63), pi. 16, fig. : 1872 

 (figure not good). — Marsh, Conch. Ex.. II. p. 110, 1887. — Dean, Amer 

 XXVI. p. 11, 1892. 



Xcristoma casta Tryox, Amer. Journ. Conch.. I, p. 249, 1865. 



Shell : Very elongate, somewhat fusiform, much compressed, 

 inclining to obliquity ; whorls 4-4^2, flat-sided and compressed ; body 

 whorl occupying from three-quarters to four-fifths the length of the 

 shell ; spire short, very acute, narrow ; aperture strongly elongate- 

 ovate, compressed in the center, the margins parallel in many speci- 

 mens, rounded anteriorly and roundly angled posteriorly ; it is some- 

 what effuse anteriorly and occasionally a little expanded ; inner lip 

 straight in most examples, the lip somewhat erect, the columellar callus 

 closely appressed to the parietal wall, but leaving, in most specimens, 

 a small chink; axis gyrate. 



Ind. 



Length. 



Breadth. 



Aperture length. 



Breadth. 





18.50 



9.00 



12.50 



5.10 mill. 



Typ e 



24.00 



11.00 



17.50 



B.00 - 



Bass Lake, 



20.50 



10.50 



14.00 



7.00 



.. 



IS. 50 



8.50 



13.50 



7.00 



U 11 



IS. 50 



9.00 



15.00 



7.50 



u 



