80 THK NALTILUS. 



species in addition to that afforded by t lie original description. It i& 

 apparently a Fem'ssia aiid dwstinpuished from the other northern 

 species by •* the delicate ribs wiiich radiate from the apex to the 

 peripliery of tlie shell." Judging from the figure, the sh«ll widens 

 posteriorly and not anteriorly, and the apex is turned to the right 

 and not, as stated by the author, to the left. Whether this be so or 

 not, the broadly ovate shape forbids its reference to the section 

 Acroloxus i^Velletia), made by Binney. Clessin's remark that the 

 form of the apex as shown in Binney 's figure recalls the European 

 forms belonging to Ancylus s. s. seems equally untenable. 



VIII. Ancylas horealis Morse (1864). PI. 6, figs. 14-16. 



I have not been able to get any authentic specimens of this species 

 for examination. Its main characteristic is stated by the author to 

 be the "fine regularly interrupted, radiating lines (which) mark the 

 surface of the shell from the apex to the border." Otherwise " the 

 species resembles A. tardus in its general form." 



The only specimens, at all referable to this species, which I have 

 seen, are those from the St. John's river at Fort Kent, Me., men- 

 tioned by Nylander (Naut., XIII, p. 105), one of which is figured. 

 They are quite close to A. tardus and possibly should be referred 

 to that species, but they are narrower and more elliptical than^ 

 the form of terrfws, which is apparently prevalent in that State. The 

 growth lines, especially near the apex, are quite strong, and where 

 these are crossed by the apical striae, the effect is that ol "fine inter- 

 rupted radiating lines," but this is confined to tiie apical region. The 

 remaining surface of the shell is irregularly rippled in the manner 

 noticed in nearly all the American species. In view of the fact that 

 in many of the species where it occurs, the radial character (except 

 at the apex) is a variable feature, the reference of these examples to 

 A. borealis seems fairly justified. The dimensions of the specimens 

 before me are as follows : 



Length (fig. 14) 3.75, breadth 2.33, alt. 1.25 min. 



Length 3.33, breadth 2.10, alt. 1.25 min. 



Length 3.50, breadth 2.00, alt. 1.33 min. 



Length 4.00, breadth 2.50, alt. 1.40 min. 



Compared with the dimensions of the type, these shells are slightly 

 narrower and not quite as high. But the difference is so slight as to 

 be easily within the lines of individual variation. 



