No. 109.] 117 



This species is larger, and not quite so gibbous as tlie last. The most 

 marked ditt'erenee between the two species consists in the much finer stride 

 of the latter; sixteen occupying the space of one-fifth of an inch, while 

 ,oulj half that number can be counted in the same space on C. hemispherica. 

 . Geological position and locality. Corniferous limestone. 



Chonetes arcuata. 



Chonetes acutiradiata (n. s.)« 



Strophomena acutiradiata, Hall : Geol. Rep. 4th Dist. N.Y. 1843, p. 171, f.3. 



This species is a true Chonetes, with strong diverging cardinal spines. 

 The surface of well-preserved speciraens is marked by strong equal rounded 

 striae, which bifurcate irregularly towards the margin. Some specimens show 

 a distinct sinus down the centre of the ventral valve ; and rarely the strige 

 are narrow and acute, with wider interstices. Ifc is probable that the original 

 described was an extreme specimen of this kind. Well preserved specimens 

 of the same shell from the original locality have the striae rarely acute, 

 though strong and rather abruptly rounded. 



Chonetes glabra ( n. s.). 



Shell semioval in outline, ventricose, hemispheric ; hinge-line 

 about equal to the greatest width of the shell : surface of the 

 ventral valve marked by obscure or slightly elevated rounded 

 striae, a few of which are more prominent near the beak ; stride 

 Increasing by bifurcation and interstitial addition, and num- 

 bering from tifty-four to sixty or more upon the margin of the 

 shell, concentrically marked by fine closely arranged striae, 



