260 



TERRESTRIAL AIR-BREATHING MOLLUSKS. 



Fig 151. 



/S. labyrinlMca, enlarged. 



may perhaps, also, have been noticetl in Mexico under the name of H. Strebeli, 

 Pfr. (see Fischer and Crosse, Moll. Mcx. et (juat.). 



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

 which characterize this species : — 



" The shell has been described as havinjj one revolvinjj tooth within the 

 aperture, and sometimes a second one terminating further within the ai)erture. 



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, 

 runninj; about a third of one volution. These 

 are plainly visible through the substance of the 

 shell. A heavy columellar tooth or rib extends 

 |Tom 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. With an ordinary magnify- 

 ing power, small swellings are seen at 



close intervals along these laminae, ^'8- ^^2. 



which, when magnified four hundred 

 diameters, are seen to be surmounted 

 with from five to ten sharp spines 

 pointing towards the apertm-e. Tliese 

 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 lamina? 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). 



Lino-ual 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.) 



Parietal laminae of S. labyrinthica. 



Strobila Hubbardi, Brown. 



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

 reddish horn-color ; whorls 4^ - 5, convex, regularly increasing, the last but 

 slif^htly descending ; umbilicus wide ; aperture quite oblique, subcircular ; 



