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 

 upj)(.'r ])arts, darker on the head and neck ; foot long and narrow ; eye- 

 ])(Mhincles long and slender; eyes black. (See Bost. Journ. Nat. Hist., 



I. n. 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 pjg 212. 



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 Eoemeri, Pfeiffer in Roemer's Texas, 455 (1849) ; 



Zeitschr. f. Mai. 1848, 117. —Reeve, Con. Icon., No. 



680. —W. G. BiNNEY, Terr. Moll., IV. 55; L. & Fr.- M. RoimeH. 



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

 ffelix dcntifera, part, Pfeiffer, Men. Hel. Viv., HI. 269 ; in Chemnitz, ed. II. 



331, PL CXXXI. Figs. 1-3, not of Binney. 

 Mesodon Eoemeri, 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. 



This 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. XL 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 



