SO Dentition of Pulmonate Mollusks. 
side ones, g, 4), and each cusp is continued into a cutting point 
(7.7, &). This last I have shaded in my figures, for the purpose 
of distinction, but no shading exists in nature. ‘The lateral 
teeth differ from the central by the suppression of the inner 
lower angle of the base of attachment and the inner cusp and 
cutting point of the tooth. Thus they are asymmetrical. As 
they pass outward, they become modified into marginals by the 
compurative enlargement of the reflection and diminution of 
the base of attachment, and by the splitting of each cutting 
point, as well as by the much diminished size of the whole tooth. 
This form of dentition is, as seen in my description, character. 
ized by quadrate marginal teeth, from which the other large 
division is distinguished by having marginal teeth of a strictly 
aculeate form (see pl. I, fig. H, three left-hand teeth). For 
the purposes of classification, this distinction of quadrate and 
aculeate marginal teeth is most important. It sometimes occurs 
that the central (see fig. K. of pl. XVI) is missing, or the laterals 
are missing (fig. H, pl. XVII). When the dentition does not agree 
with either of these two forms, I have considered it abnormal, 
and described its characters, unless the genus is found in the 
United States, when I simply refer to my descriptions in Terr. 
Moll. U.S., V. It must be remembered, however, that there 
is some variation found from the tooth referred to on pl. VIL; 
the side cusps and cutting points, especially, being in some genera 
obsolete (see all the figures on plate IX.) 
- A complete list of the lingual membranes examined by me is 
given in Bull. M. C. Z., Vol. V, No. 16, pp. 339-350. With 
the original deseription will be found the name of the person 
furnishing the membrane. ‘Those from the West Indies were 
identified by Mr. Thomas Bland. The mounted lingual mem- 
branes will be found in the Museum of Comparative Zéology at 
Cambridge. 
W. G. BINNEY, 
Burlington, New Jersey. 
