172 PROCEEDINGS OF THE ACADEMY OF 
The reflection is short, with three distinct cusps, the median long 
and slender, bulging at the sides, the outer ones very short; all 
the cusps bear cutting points in proportion to their length. The 
lateral teeth are arranged in straight transverse rows. ‘They are 
like the centrals, but unsymmetrical by the partial suppression of 
the inner side cusp and inner lower lateral expansion of the base 
of attachment, and the complete suppression of the cutting point 
to the inner side cusp. The marginals have a sole-shaped base of 
attachment, and truly aculeate cutting points, which, however, 
are bluntly bifid at their points. The marginals are in oblique, 
curving rows, gradually decreasing in size of the teeth as they 
pass off laterally. They do not first increase and then decrease, as 
in Zonites and Glandina, or not, at all events, to the same degree. 
In V. limpida, as stated below, the seventh marginal appears, 
however, to be the largest. 
In V. limpida I have counted 30—1—30 teeth, with 9 perfect 
laterals. The seventh marginal is the largest. Another gave 
39—1—39, with 10 perfect laterals. The membrane figured by 
Morse had 25—1—26 teeth, with 9 laterals. I have figured of this 
species on pl. IV. one central and its adjacent lateral in fig. 8 a, 
and the twenty-third tooth, which is one of the marginals, in 
fig. 8 6. 
Vitrina exilis has about 37—1—37 teeth, with 7 perfect laterals. 
I have given on pl. IV., fig. 7 a, one central and lateral; b,a group 
of marginals; c, an omtrenne marginal. 
Vitrina Pfeiffert has over 50—1—50, with 10 perfect aaeelle. 
I figure a group of centrals and laterals, pl. IV., fig. 6 a, and one 
extreme marginal in b. 
Genus LIMAX, Lin. 
The character of the mantle and the peculiarities of the lingual 
dentition have suggested various subdivisions of this genus into 
sections, sub-genera, and even genera. I propose, however, to 
consider the genus in its widest sense, as generally adopted. It . 
will be seen that even in the few species existing in North Ame- 
wica, there is considerable variation in the lingual dentition, espe- 
cially in the bifurcation or non-bifurcation of the marginal teeth, — 
the development of the side cusps to the central and lateral teeth, 
and the presence or absence of distinct cutting points to these 
cusps. I shall, however, simply describe the dentition of our 
