NATURAL SCIENCES OF PHILADELPHIA. 211 



ginals of H. thyroides, for instance, would hardly have been ex- 

 pected, so utterly different are they from those of albolabris. 

 Again, we should hardly have expected to find such a difference 

 in the same subgenus, as the presence and absence of side cutting- 

 points on the central and first lateral teeth. 



I will now give the count of teeth in the several species. 



Helix major, not examined. 



Helix albolabris (pi. XI., fig. 1). Outer laterals have distinct 

 side cusps as well as cutting points. Teeth 44 1 44, with about 

 12 laterals. The inner cutting points of fig. b should be bifid. 



Helix divesta, not examined. 



Helix midtilineata (pi. XII., fig. 6), 42 1 42 ; 12 laterals. 



Helix Pennsylvanica (pi. XVIII., fig. 3), 40 1 40 ; 13 perfect 

 laterals. Morse counted 120 rows of 39 1 39 teeth. 



Helix Mitchelliana (pi. XVIII., fig. 5), 49149; 18 laterals. 

 Outer laterals have side cusps and cutting points. 



Helix elevata (pi. XII., fig. 1), about 45 1 45 ; 17 laterals. 



Helix Clarki (pi. XI., fig. 6), 35135, with 15 laterals. 



Helix Christyi, not examined. 



Helix exoleta (pl.XI. f fig. 7) has 56 1 56 ; 11 perfect laterals, 

 but even the 8th tooth shows a decided modification in form. 



Helix Wetherbyi (pi. XI., fig. 2) has 35135 ; 12 laterals. 



Helix Wheatleyi (pi. XVIIL, fig. 1) has 67167, with over 

 12 laterals. 



Helix dentifera (pi. XII., fig. 8) has 32132 teeth, with 15 

 laterals. 



Helix Eoemeri (pi. XL, fig. 3) has 35135 teeth, with 12 

 laterals. 



Helix thyroides (pi. XVIIL, fig. 2) has 60160, with 11 

 laterals. 



Helix clausa (pi. XII., fig. 7) has 41141, with about 11 

 perfect laterals. 



Helix Columbiana (pi. XII., fig. 2) has 33133 teeth ; 15 

 perfect laterals. 



Helix Downieana (pi. XL, fig. 4) has 35135 teeth, with 12 

 laterals. The side cusps and cutting points are visible on the 

 second lateral tooth. 



Helix Lawi, not observed. 



Helix Mobiliana. The true species, from Baldwin County, 



