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SECTION I. LIP REFLECTED. 



Comprising all those species the margin of the aper- 

 ture of whose shell is more or less reflected. 



A. umbilicus wholly or partially covered. 



Containing species in which the centre of the base of the 

 mature shell is wholly or partially covered by the reflection 

 of the lip, at its junction with the base. 



a. Aperture destitute of tooth-like processes. 



H. abjecta, albolabris, berlanderiana, buflbniana, californiensis, clausa, 

 hortensis, major, multilineata, nickliuiaiia, pennsylvanica, polychroa, tudicu- 

 lata. 



b. Aperture furnished with one or more tooth-like processes. 



H. appressa, bucculenta, dentifera, edgariana, elevata, exoleta, germana, 

 hirsuta, inflecta, loricata, maxillata, rnonodon, palliata, spinosa, thyroidus. 



B. umbilicus not covered. 



Containing species in which the centre of the base of the 

 shell is never covered by the reflection of the lip, but in 

 which the open space, or imaginary axis about which the 

 whorls of the shell revolve, is more or less open and visible. 



c. Aperture destitute of tooth-like processes. 



H. columbiana, concava, labiosa, mobiliana, nutlalliana, pulchella, saxi- 

 cola, towusendiana, vancouverensis. 



d. Aperture furnished with one or more tooth-like processes. 



H. aurieulata, fallax, fatigiata, labyrinthica, leporina, profunda, piistula, 

 sayi, septemvolva, texasiana, tridentata, vultuosa. 



