36 



LAND AND FRESH-WATER SHELLS OF N. A. 



PART IIL 



Fig. 70. 



nutely creuulated at their apices. Cervical lappets of moderate 

 size, but not forming regular tubular aquiferous ducts ; the right 

 one plicated. Branchial lamina elongate-triangular, equal in 

 size, and arranged in a single straight row both at 

 base and tips. (Stimjjson.) Operculum with the 

 nucleus simple. 



Shell thick, solid, ovate, imperforate, spire pro- 

 duced ; whirls rounded, smooth, covered with an 

 olivaceous epidermis ; peristome simple, continuous. 



Melantbo ponderosa, Sat — Shell imperforate, globosely-ovate, 

 very thick and heavy, smooth surface hardly bro- 

 Fig- "^1* ken by the wrinkles and delicate strife of growth, 



often also with delicate revolving strise ; greenish 

 horn-color, with irregularly disposed dark stceaks, 

 marking the edges of former peristomes, milky 

 white under the epidermis ; spire short, conic, 

 apex perfect, convex ; whirls 5 or 6, very rapidly 

 increasing in length, convex, the body whirl very 

 large, equalling four-fifths the shell's length, im- 

 perforate ; aperture oval, narrowed above, slightly 

 oblique, equalling almost one-half the shell's 

 length, within white, shining ; peristome mar- 

 gined externally with darker color, simple, acute, 

 extremely sinuous, in its first half rectilinear, 

 then produced forward and rounded, then re- 

 Melantho ponderosa. treating rapidly and curving inwards and down- 



wards, thence upwards to the base of the aperture, 

 its columellar portion very much thickened, sometimes exserted sufficiently 

 to leave a narrow fissure, connected with the upper terminus by a very 

 thick and solid callus, which enters beyond sight within the aperture, and 

 at the upper portion is produced into a prominent Lithasia-like thickening, 

 between which and the peristome is a deep sinus. Length of the axis 33, 

 greatest breadth of body whirl 27 ; length of aperture 28, greatest breadth 

 19 mill. 



Operculum elongate-ovate, narrow above, convex, margin thin, horny, 

 concentric, nucleus near the columella. 



Paludina ponderosa, Say, 1821, J. A. N. S. II, 173; Am. Conch. Ill, pi. 

 XXX, f. 1 (1831) ; ed. Binney, p. 68. 184, pi. xxx, f. 1 ; ed. Chexu, 

 41, pi. xi, f. 5.— Haldeman, Mon. p. 13, pi. iv (1840).— De Kay, 

 N. Y. Moll. p. 81) (1843) (exc. syn. heterostropha) . — Deshayes in 

 Lam. ed. 2, VIII, p. 51G (1838) ; ed. 3, III, p. 453, excl. P. decisa.— 

 KtJSTER in Chemnitz, ed. 2, p. 14, pi. iii, f. 1-4, p. 20, pi. iv, fig. 6.— 



