AOBRh 
NATURAL SCIENCES OF PHILADELPHIA. 161 
cusp. The other figures are clr awn from below, to show the base 
of attachment. 
M. Vancouverensis, drawn by Morse, has 22—1—22 teeth, two 
other membranes examined by me gave 24—-1—24, one other 
18—1—18. WM. concava has given 20—1—20, 23—1—23, and 
95—1—25. Of M. Duranti I have counted but one membrane 
having 18—1I—18. <A single membrane of I. Voyana had 24— 
1— 24 teeth. 
To sum up the characters of the dentition of Macrocyclis it 
may be said to be intermediate between ‘Glandina and Zonites, 
differing from the former in the presence of the transition teeth 
from true laterals to true marginals, differing, however, from the 
latter by the absence of true lateral teeth. 
Genus ZONITES, Montf. 
In the preceding genus Glandina we found only the aculeate 
form of teeth or pure marginals ; in Macrocyclis we found in addi- 
tion to these marginals a few showing a modification of this type, 
being the transition teeth from marginals into laterals. In the 
present genus, Zonztes, we find for the first time the lateral teeth 
in their full development. Thus we have the three forms of teeth, 
centrals, laterals, and marginals, all present, and apparently a 
generic characteristic. It will be noticed, however, that in lexvi- 
pron 5. 
Gyan view of oniion of ee OD nias 
gatus' (pl. II., fig. 1, 2) there is no perfect lateral, the first tooth 
showing a decided modification or transition into the marginals. 
Thus we cannot say that in all species of Zonites there are pure 
lateral teeth. It will be seen below that in some species the num- 
ber of laterals is reduced to two. 
1 See also cellarius. 
