NATURAL SCIENCES OF PHILADELPHIA. 193 
Genus ARIOLIMAX, Morch. 
Jaw thick, slightly arcuate, ends but little attenuated, blunt ; 
low, wide: anterior surface with numerous stout ribs, denticulating 
either margin. The number of ribs varies 
in the several species, and in different indi- 
viduals of the same species. Fig. 39, drawn 
from the true northern A. Columbianus, has 
18 ribs; another specimen, supposed to be 
the same species, has about 12. (See Proc. 
Ac. Nat. Se. Phila. 1874, pl. II., fig. 11.) A. 
Californicus has given 13 and 14 ribs. A. niger has been de- 
scribed by Dr. Cooper with 20, but I found only 8 in one specimen 
which I refer to that species. 
Fig. 498 of p. 279, L. and Frw. Shells N. A., I, gives the general 
arrangement of the teeth upon the lingual membrane. It is drawn 
from the true northern .4. Columbianus. On pl. V., fig. 6, I have 
given more detailed figures of the dentition of a specimen I refer 
to this species. It will be seen that the central teeth have a base 
of attachment longer than wide, with expanded lower angles, and 
incurved lower margin ; the upper margin is reflected; the reflec- 
tion is large, broad, and has a short, stout median cusp, bearing 
a long, stout cutting point; the side cusps of the reflection are 
subobsolete, but there are well-developed triangular cutting points. 
The laterals are like the centrals, but unsymmetrical by the sup- 
pression of the inner lower lateral expansion to the base of attach- 
ment, and the inner side cutting point, the inner side cusps being 
still subobsolete. 
The change from lateral to marginal teeth is shown in 6 and c, 
the median cusps and cutting point being greatly developed, and 
sometimes (¢) having a side cusp and cutting point; the base of 
attachment is still narrower than in the first laterals. The mar- 
ginals are shown ind and e. They are about as high as wide, the 
reflection equals the base of attachment and bears an extremely 
long, blunt, stout, oblique cutting point, with a side spur upon 
the last, in the extreme marginals developed into a short, stout, 
side cutting point. The cutting point of the marginals by its 
great development forms the chief characteristic of the membrane ; 
it is well shown in profile (fig. f.). There were 22 perfect laterals 
in this specimen. The figure referred to above shows only 12 late- 
rals, with 113 rows of 56—1—56 teeth each. 
Jaw of Ariolimax 
Columbianus. 
