MESODON. 



325 



Fig. 209. 



M. Clarki. 



ing the umbilicus entirely ; one elongated, white denticle on the parietal wall 

 of the aperture. Greater diameter 14, lesser 13 mill.-, height, 9 mill. 



Helix Clarkii, Lea, Proc. Acad. Nat. Sc. Philad., 1858, 

 41; Journ. — ; Obs., XI.-138, PI. XXIV. Fig. 111. 

 — W. G. Binney, Terr. Moll., IV. 53, PI. LXXVII. 

 Fig. 10 ; L. & Fr.-W. Sh., I. 143 (1869). 



Xolotrema Clarkii, Tryon, Am. Journ. Conch., III. 48 

 (1867). 



Cherokee County, North Carolina; also in Georgia 

 and Eastern Tennessee. It is a species of the Cumber- 

 land Subregion. 



The lower figure was photographed on to the wood. 



Jaw as usual, arcuate, ends attenuated, blunt ; an- 

 terior surface with about 14 stout, separated ribs, den- 

 ticulating either margin. 



Lingual membrane long and narrow. Teeth about 35 — 1 — 35. Centrals 

 with a stout, short, median cusp, bearing a very short, blunt cutting point, the 

 outer cusps subobsolete. Laterals 15, like the centrals, but asymmetrical. 

 Marginals wide, low, with one inner, short, broad, sharply bifurcated cutting 

 point, and one shorter, outer, bifurcated cutting point ; those figured are very 

 bluntly denticulated ; on other portions of the same membrane the cutting 

 points are much more developed and more acute (PI. VIII. Fig. I). 



The genital system (PI. XI. Fig. G) is peculiar in several respects. The 

 ovary is very slender, and equals about one half the length of the oviduct. 

 The epididymis is highly developed, greatly convoluted, stout, four times the 

 length of the ovary. The oviduct is convoluted. The prostate is greatly de- 

 veloped. The penis sac is short, cylindrical, entering the vagina near its base, 

 and receiving both vas deferens and retractor muscle at its apex. The genital 

 bladder is small, oval, with a short duct entering the vagina about the middle 

 of its length. The vas deferens is swollen on leaving the prostate. Testicle 

 not observed. 



Mesodon Christyi, Bland. 



Shell imperforate, depressed, rather solid, with numerous oblique rib-like 

 stria?, dark horn-colored ; spire short, obtuse ; whorls 4^, rather 

 convex, the last descending at the aperture, slightly angular at 

 the periphery, constricted, above gibbous ; base convex, exca- 

 vated in the middle ; aperture depressed, with a strong, oblique, 

 lamelliform parietal tooth; peristome reflected, with a white caHus 

 within. Greater diameter 10, lesser 8 mill.; height, 4i mill. 



Helix Christyi, Bland, Ann. N. Y. Lye, VII. 117, PI. IV. Figs. 5, 

 6 (1860). — W. G. Binney, L. k Fr.-W. Sh., I. 141 (1869). 

 Mesodon Christyi, Tkyon, Am. Journ. Conch., 111. 40 (1867). 



Fig. 210. 



JW. Christyi. 



