184 A MANUAL OF AMERICAN LAND SHELLS. 



Jaw arcuate, broad in center, greatly attenuated and blunt at ends ; 

 concave margin smooth, with a slight median projection. 



The lingual membrane examined (Terr. Moll., V, Plate III, Fig. N) 

 had 14-1-14 teeth, with 2 perfect laterals. Morse gives 68 rows, with 

 15-1-35 teeth, also 2 perfect laterals. 



Family HELICID^. 



ACAKTIII^flJLA, Beck. 



Animal heliciform ; mantle posterior; other characters as in Pa^iiZa 

 (see below, Fig. 184). 



Shell perforated, globosely turbinated, with a brownish plicately 

 ribbed or aculeate epidermis ; whorls 4-5 ; aperture rounded ; peri- 

 stome thin, somewhat expanded, its terminations approached. 



In Europe this genus is found at the north, but one species ranges 

 as far south as Palermo. Our single species is probably circumpolar, 

 common to the three continents. 



We have but one species within our limits, A. harpa^ whose jaw and 



lingual dentition have been described and figured by Morse. Judging 



from his figure (Fig. 181) and text, the anterior surface of 



Fig. 181. 



the jaw seems to have subobsolete ribs which mark the 

 lower margin ; it is low, wide, strongly arched, with 

 Jaw of 4.Aorpa. blunt, scarccly attenuated ends; cutting edge with a 



(Moi'ae.) 



wide and very slightly produced, broad, median projec- 

 tion ; transversely and longitudinally striate. 

 Lingual membrane long and narrow; 120 rows of 17-1-17 teeth. 



l>iiii;ual (Uiititiou of J. liaiua. (^Im 



with 6 perfect laterals. The centrals h.ive a square base of attach- 

 ment, the upper margin squarely reflected; the reflection is very 

 small, tricuspid, the side cusps very small, blunt, the median cusps 

 very long and narrow, not reaching the lower edge of the base of at- 



