80 A MANUAL OF AMERICAN LAND SHELLS. 



There are 32 rows in one lingual examined of M. Vancouverensis. 

 (See Fig. 45.) The rows of teeth are arranged en chevron. Each row 

 is divided by the median line into two irregular crescents, the teeth 

 rapidly increasing and curving in a backward direction, and then 

 gradually decreasing in size and curving forward. In M. Vancou- 

 verensis the sixth tooth is the largest. The teeth of MacrocycUs, as 

 also of Glandina, are separated, not crowded, as in the Helicidoe. 

 The central tooth is seen with some diflBculty by the microscope. I 

 am confident, however, that I have drawn it correctly for the various 

 species. In M. Yancouverensis (Plate I, Fig. B, T. M. V., see also 

 below Fig. 45,) the base of attachment is small, triangular, the apex 

 pointed forward, the angles bluntly rounded, somewhat incurved at 

 base, and bears a delicate, simple, short, slender cutting point, reach- 

 ing from about its center to near its base. This cutting point was not 

 figured by Morse, and, indeed, was observed by me only on a few of 

 the central teeth, and then with difSculty. In M. concava (Plate I, 

 Fig. C) the central tooth has a larger base of attachment, the apex of 

 the triangle is truncated and incurved, the base is more incurved, the 

 outer lower corners more expanded and pointed, the cutting point 

 more developed, with distinct lateral expansions like very slightly 

 developed subobsolete side cusps. In M. Voyana (Plate I, Fig. D) 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 seem to be 

 no distinctly developed cusps bearing these cutting points. In M. 

 Duranti (Plate I, Fig. E) the central tooth has a base of attachment 

 somewhat like that of M. Vancouverensis^ but longer, and with incurv- 

 ing sides ; the cutting point is the same. I have also examined the 

 lingual membrane of M. sportella (Plate XV, Fig. K) which may be 

 merely a variety of Vancouverensis ; its dentition is quite the same. 

 The other species mentioned above are readily distinguished one from 

 another by the form of their central teeth. 



The side teeth of MacrocycUs at first sight, especially when seen from 

 below, appear to be of the purely aculeate type, as the marginals in 

 Zonites and Limax. From this, one is inclined to consider them all as 

 marginals, and to declare that no true lateral teeth exist, thus making 

 MacrocycUs to agree with Glandina in this particular also. A more care- 

 ful study shows us that the teeth nearest the median line are modified 

 from the aculeate type, though they do not have the distinct form of 



