74 POLYGYRA. 



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P. implicata (Beck) Mart, iii, P. ventrosula Pfr., iii, 136. 



[133. v. liindsii Pfr., iii, 136. 



P. oppilata Morel, iii, 133. P. texasiana Moric., iii, 135. 

 P. dysoni Shuttl., iii, 132. tamaulipasensis Lea. 



dorfeuilliana Pfr. not Lea. tridonia Beck. 



P. chiapensis Pfr., iii, 138. P. triodontoides Bid., iii, 135. 



P. mooreana W. G. B., iii, 135. P. behri Gabb., iii, 134. 



v. tholus W. G. B., iii, J35. P. ariadna? Pfr., iii, 132. 

 P. yucatauea Morel., iii, 146. couchiana Lea. 



v. helictomphala Pfr., iii, 130. P. acutedentata W. G. B., iii, 

 P. plagioglossa Pfr., iii, 133. loisa W. G. B., iii, 134. [134. 



P. dissecta v. Mart., viii, 151. quinqnedentata F. & C. 



P. couloni Shuttl., iii, 134. v. unguifera Mouss., iii, 132. 



P. bicruris Pfr., iii, 136. P. anilis Gabb., iii, 130. 



P. richardsoni v. Mart., viii, 151. P. hippocrepis Pfr., iii, 134. 



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P. johannis Poey, iii, 130. notata Poey. 



Section Triodopsis Rafinesque. 



Triodopsis plus Mesodon of authors. 



Shell varying from depressed to globose-couoidal, umbilicate or 

 imperforate ; surface generally striated ; whorls 5-6, the last wider, 

 more or less deflexed in front. Aperture lunate, typically obstructed 

 by three teeth, two on the lip, one on the parietal wall ; but any or 

 all of the teeth often absent. Type P. tridentata Say, pi. 30, fig. 8 

 (see also pi. 30, figs. 9, 10, P. appressa; pi. 30, figs. 13, 14, P. albo- 

 labris var. maritima; pi. 30, figs. 17, 18, P. sayi). 



Jaw sculptured with numerous moderately spaced ribs (pi. 30, fig. 

 19, P. sayi; pi. 30, fig. 21, P. kiawaensis; pi. 21, fig. 11, P. 

 albolabris). 



Radula having (1) ectocones with cutting-points developed on 

 central lateral and marginal teeth, as in P. tridentata, pi. 30, fig. 11, 

 and P. albolabris, pi. 30, fig. 16, or (2) no side cusps or cutting- 

 points whatever on any of the teeth, as in P. clausa, pi. 30, fig. 15. 



Genital system as described for the genus (pi. 30, fig. 12, P. 

 inflecta; pi. 30, fig. 20, P. clausa; pi. 21, figs. 12-16, P. albolabrii). 

 In P. albolabris Say (pi. 21, figs. 12-16) the lower third of the penis 



