260 



TERRESTRIAL AIR-BREATHING MOLLUSKS. 



Fig 151. 



may perhaps, also, have been noticed in Mexico under the name of H. Slrebeli, 



Pfr. (see Fischer and Crosse, Moll. Mex. et Guat.). 



Mr. Morse has lately given the following description of the internal laminae 



which characterize this species : — 



" The shell has been described as having one revolving tooth within the 



aperture, and sometimes a second one terminating farther within the aperture. 



I have always found this second one constant, 

 and also a third one, but slightly raised between 

 these two. At the base of the shell and far 

 within the aperture are two more revolving ribs, 

 running about a third of one volution. These 

 are plainly visible through the substance of the 

 shell. A heavy columellar tooth or rib extends 

 from a slight distance within the aperture, nearly 

 one volution back. This columellar tooth thick- 

 ens the substance of the shell in the umbilical 



region, and causes a distinct fold without the shell. A most singular feature is 



revealed in the structure of the parietal laminae. 



ing power, small swellings are seen at 



S. labyrinlhica, enlarged. 



With an ordinary magnify- 

 Fir- 152. 



Parietal laminae of 5. labyrinthica. 



close intervals along these laminas, 

 which, when magnified four hundred 

 diameters, are seen to be surmounted 

 with from five to ten sharp spines 

 pointing towards the aperture. These 

 swellings appear to coincide in num- 

 ber and position with the raised ribs 

 without the shell, though they are 

 not formed at the same time ; for as 

 these laminae approach the aperture 



they become attenuated and disappear. The surface upon which these laminae 

 rest is granulated, and not smooth, as is generally the case with the interior of 

 shells. It is difficult to imagine the use of these spiny projections, unless they 

 may act in some way as points of resistance to the animal for the support of a 

 very heavy shell." 



Jaw (see p. 258). 



Lingual membrane with 78 rows of 13 — 1 — 13 teeth each; centrals tricus- 

 pid, central cusp very long ; laterals of same shape, but bicuspid ; marginals 

 low, broad, serrated. (PI. V. Fig. O.) 



Strobila Hubbardi, Brown. 



Shell umbilicated, depressed, thin, obliquely striated above, smooth below, 

 reddish horn-color ; whorls A\ - 5, convex, regularly increasing, the last but 

 sbVhtly descending ; umbilicus wide ; aperture quite oblique, subcircular ; 



