MESODON. 329 



Readily distinguished from the allied species by the very angular and broad 

 reflection of the peristome. 



Animal grayish on the sides and posterior extremity, brownish on the 

 upper parts, darker on the head and neck ; foot long and narrow ; eye- 

 peduncles long and slender ; eyes black. (See Bost. Journ. Nat. Hist., 

 I. PI. X.) 



Jaw as usual in the genus ; 14 ribs. 



Lingual membrane (PI. VIII. Fig. J) with 32 1 32 teeth, with 15 laterals. 



Mesodon Roemeri, PFEIFFER. 



Shell with a narrow, or partially covered umbilicus, sometimes imperforate, 

 depressed, rather thin, closely striated, rather transparent and smooth, horn- 

 colored ; spire slightly elevated; suture lightly impressed; 

 whorls 5, rather convex, increasing slowly, the last one Firr 2 i2 



subcarinate at its periphery, scarcely descending ; aper- 

 ture lunar, oblique, generally slightly contracted by a 

 parietal denticle which obliquely enters the mouth of the 

 shell; peristome white, thickened, the upper portion hardly 

 expanded, reflected below, and at the columellar junction 

 spreading into a thin, partial covering to the umbilicus. 

 Greater diameter 21, lesser 18 mill. ; height, 10 mill. 



Helix Roemeri, PFEIFFER in Koemer's Texas, 455 (1849) ; 



Zeitschr. f. Mai. 1848, 117. REEVE, Con. Icon., No. 



680. W. G. BINNEY, Terr. Moll., IV. 55; L. & Fr.- M. R ac meri. 



W. Sh., I. 146, Fig. 250 (1869). 

 Helix dcntifcra, part, PFEIFFER, Mon. Hel. Viv., III. 269 ; in CHEMNITZ, ed. II. 



331, PI. CXXXI. Figs. 1-3, not of BINNEY. 

 Mesodon Roemeri, TRYON, Am. Journ. Conch., III. 43 (1867). 



Near New Braunfels, Texas ; Washington County, Williamson County, 

 Bosque County, and Colorado River, Texas. A species of the Texas Subregion. 



Tliis species was formerly confounded by Pfeiffer with dentifera, an authen- 

 tic specimen of which he had not seen. It is quite a distinct species, and in- 

 habits a distinct geographical region. It may be distinguished from dentifera 

 most readily by attention to the following particulars : Its umbilicus is gen- 

 erally but partially covered, while dentifera is always imperforate ; its color is 

 lighter, its surface smoother, and, above all, its peristome is not so broadly 

 reflected ; it is also distinctly subcarinate at the periphery. 



Jaw as usual ; 7 ribs on one, 9 on another specimen examined. 



The lingual membrane (PI. VIII. Fig. C) has 35 1 35 teeth, with 12 lat- 

 erals. A few of the last laterals may have side cusps and cutting points. 



The genitalia are figured on PI. XI. Fig. J. The oviduct is scarcely convo- 

 luted. The genital bladder is large, oval, with a long, large duct. The penis 

 sac is short, stout, of about equal breadth throughout, ending in a stout oval 



