BULIMULUS. 



209 



aperture the peritreme is margined with a broad white callus. 

 Under such circumstances it bears considerable resemblance to 

 B. alternatus, but the interior of the aperture never has the dark 

 coloring of that species, nor is the columella furnished with the 

 tooth-like fold. It is especially in Texas that it is found in such 

 perfection. I have no doubt that the specimens figured on pi. 

 51 a of the Terrestrial Mollusks came from that State. 



It is this last described form of the species which has been 

 called Bulimus lactarius. I have seen no authentic specimen, 

 but from Pfeiffer's description (see Terr. Moll. IV, 128), and his 

 reference to all but the lower figure of plate 51a (Mon. lY, 416), 

 there remains no doubt of the identity of the two. 



The variation in the globoseness of the whirls, and consequent 

 outline of the shell, may be judged from the following measure- 

 ments of two specimens : diam. 18, length 25 ; diam. 7, length 

 19 mill. 



Of Bulimus Uquahilis and confinis I have given the original 

 description and a fac-simile of the original figures in 

 the fourth volume of the Terrestrial Mollusks. 



The jaw of Bulimulus alternatus is narrow, 

 strongly arched, with distant anterior ribs, denticu- 

 lating the concave margin. It does not agree with 

 the description of the jaw of the subfamily Orlha- 

 licinse (p. 212). 



The lingual membrane consists of 94 rows of teeth, 25 — 1 — 25 

 in each row. Central teeth long, tricuspid, laterals bicuspid, the 

 cusps modified as the teeth pass off laterally. 



Fiff. 360. 



Fig. 361. 



Lingual dentition of Bulimulus dealbatus. 



14. December, 1868. 



