NATURAL SCIENCES OF PHILADELPHIA. 



167 



Jaw of Z. milium. 

 [Morge.] 



Fig. 7. nels are probably worn by the greatly de- 



veloped central tooth of the lingual membrane. 

 I do not agree with Morse in considering the 

 great development of the central tooth, and 

 the channels on the jaw as generic characters. 

 Z. Binneyanus is described by Morse with 60 rows of 23 1 23 

 teeth, with two perfect laterals which have a form of inner side 

 cutting point. 



On pi. XVII., fig. 13, I give a figure of the teeth on a membrane 

 examined by me, kindly furnished by Mr. Anson Allen, of Orono, 

 Maine. I find 19119 teeth, with 3 laterals. I doubt there being 

 any inner cutting points to the lateral teeth. 



Z. ferreus (pi. XVII., fig. 9), is described by Morse with 39 



rows of 20120 teeth. I 

 found 20120 teeth also, 

 with 2 laterals. The cen- 

 tral tooth is greatly de- 

 veloped, and the jaw (fig. 

 8) has vertical median 

 channels, or groves, as in 

 Z. milium (see above, fig. 7). 

 Z. conspectus, not examined. 

 Z. exigitus. I give here a copy of Morse's figure, having 69 



Fisr. 8. 



Jaw of Z. ferreus. [Morse.] 



Fig. 9. 



Z. exiguu8. 



rows of 16 1 16 teeth, with 4 perfect laterals. The transition 

 teeth and several of the adjoining marginals are described \>y 

 Morse with a small side spur to their cusps, apparently of the 

 same type as I have figured for Macrocyclis Vancouverensis (pi. 

 I., fig. 4). On pi. XVII., p. 14, 1 give a drawing of a specimen 

 examined by me. I found 16 1 16 teeth with 5 laterals. 

 Z. chersinellus, not examined. 



