NATURAL SCIENCES OF PHILADELPHIA. 159 



Fi<r. 4. divided by the median 



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 J/. 

 Vavcouverensis the sixth 



Liugual deatition of Mucrncyclis Vancouveren.tis. tOOtll is the laro"est. One 



of these subcrescentic 

 rows is shown in fig. 4, copied from L. and Frw. Sh., I., drawn 

 b3' 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 Helicinse. The central tooth is seen with some difficulty 

 \)y the microscope. I am confident, however, that I have drawn 

 it correctly for the various species. In M. Vancouverensis (pi. 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 31. concaua (pi. 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 M. Voyana (pi. 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- 

 ranti the central tooth has a base of attachment somewhat like 

 that of 31. Vancouve7'ensis, but longer, and with incui'ving sides; 

 the cutting point is the same. I have not examined the lingual 

 membrane of 31. 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. 



