478 PROCEEDINGS OF THE ACADEMY OF [Juty, 



The raclula of a San Marcos specimen (PI. XXXVIII, fig. 6) has 

 65, 5, 1,5, 65 teeth, the cusps, especially of the centrals, being longer 

 and narrower than in any other of our species of Omphalina. Two 

 radulae examined. 



In an individual from Mablevale, Ark. (PI. XXXVIII, fig. 4), 

 there are about 55, 5, 1, 5, 55 teeth, the centrals somewhat less 

 lengthened. Counted in another place, I found 53, 5, 1, 5, 53 teeth 

 on the same raclula. 



Binney records 57, 1, 57 teeth with 6 perfect laterals. The locality 

 of the snail he examined was not stated. Except in having somewhat 

 longer cusps, the radulse I prepared differ very little from 0. cuprea. 



Genus MESOMPHIX ('Eaf.') Beck. 



Beck, Index Molluscorum, p. 7 (1837), for M. virginalis B. (undescribed), 

 M. fuliginosa Griff., M. ivalkeri Gray, M. Icevigata Raf., M. elliptica 

 Mich, and M. olivetorum Gm. 



Herrmannsen, Inclicis Generum Malacozoorum Primordia, II, p. 40, "typus 

 Helix laevigata Raf." (July 17, 1S47). 



The shell is like Omphalina, except that it is more depressed, with 

 a much smaller umbilicus and the embryonic whorls are ribbed or 

 striate radially in most species. 



External anatomy as in Omphalina. Genitalia differing from 

 Omphalina by the development of a flagelliform gland terminal on 

 the pe?iis. The epiphallus is distinctly differentiated from the vas 

 deferens. Vaginal gland wanting. Jaw reddish-brown or black, 

 very opaque, with a small median projection. 



Radula with the basal-plate of the central tooth contracted in the 

 middle; lateral teeth few, to 4. Marginal teeth as in Omphalina. 



Type M. Icevigata. 



This genus is well differentiated from Omphalina by the presence 

 of a flagelliform penial gland, a very unusual structure in American 

 Znnitidce. This gland is long and slender in M. subplana 

 (PI. XXXVII, fig. 7, p.g.), shorter and stout in M. Icevigata (fig. 10). 

 The shell often bears a diagnostic feature in its scuptured apex. 

 The jaw in all the species examined (M. Icevigata, subplana, rugeli, 

 andrewsce and inornata) is remarkable for its dark or black color. In 

 Omphalina the jaw is pale yellow, so far as observed. 



These features are an advance beyond the morphology of Ompha- 

 lina, being, as it were, superposed upon the Omphalinoid organization. 

 The radula also is more specialized by the partial or complete elimina- 

 tion of lateral teeth. 



In describing the genus Mesomphix, Rafinesque mentioned no 



