MESODON. 317 



uals, and indeed in all specimens from certain localities. In its most perfect 

 condition it is often subconical. It is subject to some irregularities in the form 

 of the aperture, and there is sometimes an indication of pale bands in the epi- 

 dorniis of the body-whorl. 



A large individual had the greater diameter 48, lesser 40 mill. ; height, 

 30 mill. 



Animal : head, upper part of neck, tentacles, and eye-peduncles, ferruginous ; 

 eyes black; foot rusty, the sides more or less shaded with blue by the fluids of 

 the animal, which are visible through its semi-transparent substance. Eye- 

 peduncles short, in proportion to the size of the animal, and robust, their situ- 

 ation, when retracted, marked by brown lines. Foot large and thick. Genital 

 orifice indicated by a slight prominence. Superficial glands large and distinct. 

 On the centre of the back is a line of them, of an oblong narrow shape, with a 

 furrow on each side ; those on the sides and posterior part of the foot, when 

 examined by a microscope, exhibit numerous subcutaneous white dots, or 

 points, arranged in clusters. Length equalling twice the diameter of the shell 

 (see Bost. Journ. N. IL, I. PI. 1). 



Jaw and lingual membrane as in alholahris. PI. VIII. Fig. G, shows the 

 latter. 



Genitalia also same as in alholabris (see Proc. Phila. Ac. Nat. Soc, 1876, 

 189, PI. VI. Fig. 1). 



I still retain as a distinct species the form known as major, though the study 

 of the limits of variation in the shells of our species has led me strongly to 

 doubt its specific value. I am inclined to consider it as a greatly developed 

 form of albolahris, caused by certain peculiarly favorable local causes in a cer- 

 tain portion of the Southern Region. 



Mesodon albolabris, Say. 

 Vol. in. PL II. 



Shell imperforate, convex; epidermis immaculate, of a uniform yellowish- 

 brown, russet, or light chestnut-color ; whorls 5-6, with fine parallel striaj 

 i*unning obliquely across them, and spirally striated with very minute and deli- 

 cate, but distinct, wavy, impressed lines, which are most apparent on the back 

 of the reflected peristome ; suture well marked and distinct ; aperture con- 

 tracted by the peristome ; peristome white, flattened in the plane of the mouth 

 abruptly and very widely reflected ; umbilicus of the mature shell covered by 

 the reflected peristome, which is continued to the base of the shell. Greater 

 diameter 30, lesser 26 mill. ; height, 17 mill. 



Belix albolabris, Say, Nich. Encycl., PI. I. Fig. 1 (1817-1819); Journ. Acad. 

 Nat. Sci. Phila., IL 161 (1821); Ameiican Conch., No. 2, PL XIIL (1831); 

 BiNXFA-'s ed., 21, PL LXIX. Fig. 1. — Cuenu, Bibl. Conch., IlL 21, PL 

 III. Fig. 3, a. — Adams in Thompson's Vermont, I. 158, with wood-cut. — 

 Eaton, Zobl. Text-Book, 193 (1826). — F^iussac, Tab. Syst., 36 ; Hist., PL 



