42 



LAND AND FRESH-WATER SHELLS OF N. A. [PART I. 



H. conspecta differs from Helix asteriscua in having an ele- 

 vated spire and a smaller umbilicus. The rib-like striai are more 

 numerous, but scarcely raised above the surface of the shell, 

 which, under the microscope, is very similar to that of H. 

 asteriscus. 



Hyalina exigua also has very prominent ribs, but they are 

 independent of the stri» of growth and run obliquely to them. 



Fig. 63. 



Hyalina exigua, 

 enlarged. 



Hyaliua exigua, Stimpson. — Shell broadly umbilicatecl, depressed, 

 pellucid, greeuish horn-color, marked with delicate revolving lines, and 

 distant longitudinal ribs obliquely decussating the incre- 

 mental stripe ; spire scarcely elevated, apex free from 

 strife ; whirls three and one-half, convex, the last rounded, 

 widely umbilicated below ; aperture oblique, transversely 

 rounded, remote from the axis ; peristome simple, acute, 

 its columellar extremity not reflected. Greater diam. 2^, 

 height i mill. 

 Helix exigua, Stimpson, Proc. Bost. Soc. Ill, 175 (1850). — Gould, T. M. 

 Ill, 16.— W. G. BiNXEY, T. M. IV, 102, pi. Ixxvii, f, 19.— Pfeiffer, 

 Mon. Hel. Viv. Ill, 102.— Morse, Amer. Nat. I, 543, f. 34 (1867). 

 Helix annulata, Case in Sill. Journ. [2] 1847, III, 101, f. 1-3; Ann. and 



Mag. Nat. Hist. 1847,338, preocc— Pfeiffer, Mon. Ill, 103. 

 Helix striatella, junior, teste Gould, Sill. Journ. Ill, 276 (1847). 

 Pseudohyalina exigua, Mokse, Journ. Portl. "Soc. I, 16, pi. 11, f. 8 ; pi. vii, 

 f. 33 (1864).— Tryon, Am. Journ. Conch. II, 265, pi. iv, f. 57 (1866). 



Fig. 64. 



Surface of 

 Hyalina exigua. 



laterally. 



Canada, New York, and New England ; Tawas 

 Bay, Mich. 



Fig. 64 shows the peculiar sculpturing of this 

 species. 



The lingual membrane has 69 rows of 16 — 1 — 16 

 teeth each ; centrals with one long, slender, and 

 two short cusps ; laterals of same shape, but bi- 

 cuspid ; unclni thorn-like, aculeate, recurved, 

 diminishing greatly in size as they pass off 



Fig. 65. 



Lingual dentition of Hyalina exigua, [Morse.] 



