NATURAL SCIENCES OF PHILADELPHIA. 159 
Fig. 4. divided by the median 
ee line into two irregular 
crescents, the teeth rap_ 
idly increasing and curv. 
ing in a backward direc- 
tion, and then gradually 
decreasing in size and 
curving forward. In JZ. 
pee eles e Vancouverensis the sixth 
Lingual dentition of Macrvcyclis Vancouverensis. tooth is the largest. One 
of these subcrescentic 
rows is shown in fig. 4, copied from L. and Frw. Sh., I., drawn 
by Morse. ‘This figure, however, must not be used to judge of the 
shape of the separate teeth, better shown in plate I. The teeth 
of Macrocyclis, as also of Glandina, are separated, not crowded, 
as in the Helicinz. The central tooth is seen with some difficulty 
by the microscope. I am confident, however, that I have drawn 
it correctly for the various species. In J. Vancouverensis (pl. I., 
fig. 4), the base of attachment is small, triangular, the apex 
pointed backward, the angles bluntly rounded, somewhat incurved 
at base, and bears a delicate, simple, short, slender cutting point, 
reaching from about its centre to near its base. This cutting 
point was not figured by Morse (see above fig.), and, indeed, 
was Observed by me only on a few of the central teeth, and then 
with difficulty. In MM. concava (pl. I., fig. 3) the central tooth 
has a larger base of attachment, the apex of the triangle is trun- 
cated and incurved, the base is more incurved, the outer lower cor- 
ners more expanded and pointed, the cutting point more devel- 
oped, with distinct lateral expansions like very slightly developed 
subobsolete side cusps. In J. Voyana (pl. I., fig. 5), the central 
tooth has a long, narrow, quadrangular base of attachment, incurved 
above, below, and at sides, and bears near its base three small, 
sharp cutting points, the median the largest; there seems to be no 
distinctly developed cusps bearing these cutting points. In M. Du- 
rantt the central tooth has a base of attachment somewhat like 
that of MZ. Vancouverensis, but longer, and with incurving sides ; 
the cutting point is the same. I have not examined the lingual 
membrane of MM. sportella, which may be merely a variety of Van- 
couverensis. The other species mentioned above are readily distin- 
guished one from another by the form of their central teeth. 
