XXV111 CLASSIFICATION OF HELICES. 



ical affinities, even when as in the case of Pleurodonte (p. 86), I 

 could not at the time of writing, see the slightest connection between 

 the clearly expressed organic characters, and the apparently anom- 

 alous distribution. 



CLASSIFICATION OF SNAILS WITH JAW AND A HELICOID OR 

 ZONITOID SHELL. 



Key to families. 



[It will readily be understood that for purposes of a key, only the 

 most obvious peculiarities are chosen ; too much space would be re- 

 quired were the diagnostic characters of all organs to be given]. 



I. Foot-edges with no trace of pedal grooves ; no tail gland ; sole 

 undivided. Side teeth unicuspid, thorn-shaped, with narrow 

 basal-plates. Shell with simple lip and without opaque mark- 

 ings, SELENITID.E. 



.II. Foot margin defined by a pedal groove. Shell sharp-lipped. 



a. Marginal teeth with narrow, elongated basal-plates, and 

 either unicuspid and thorn-shaped by suppression of side 

 cusps, or bicuspid by elevation of outer on middle cusp. 

 Tail gland often present, and sole frequently tripartite, 



ZONITIDJK. 



b. Marginal teeth with wide, short and squarish basal-plates, 

 with one or several cusps, the outer cusp never elevated on 

 middle cusp. Shell with opaque, brown coloring or flam- 

 mules, usually rib-striate, the lip thin, unexpanded and 

 sharp, ENDODONTID^E. 



III. Foot-edges without pedal grooves; no tail gland. Marginal 

 teeth with wide, short, squarish basal-plates and one or several 

 cusps, the outer cusp never elevated on middle cusp. Shell 

 usually with expanded or reflexed lip, HELICID^E. 



This series of families is allied on one side to groups which have 

 undergone degeneration of the jaw, such on Rhytididct, and on the 

 other to the families to be monographed in succeeding volumes of 

 the MANUAL. The Selenitidce and Zonitidce will not further be con- 

 sidered in this volume, with the exception of a single genus of the 

 latter (TROCHOMORPHA, page 1), which Tryon and Fischer errone- 

 ously intercalated among the Patuloid snails. 



