THE WEST AT^IERICAN MOLLUSKS OF THE GENUS 



NODULUS 



By Paul Bartsch 



Assistant Curator, Division of Mollusks, U. S. National Museum. 



The known members of this genus were formerly referred to Onoha. 

 That group, however, has feeble axial ribs as well as spiral sculpture. 

 In Nodulus we find a very characteristic oblique aperture; axial ribs 

 are never present and spiral sculpture, if at all present, is reduced to 

 exceedingly fine striations. 



Doctor Dall, in a paper on Mollusks of Bering Sea and vicinity,* 

 was the first to report members of this group from the West Coast of 

 America. In this publication he described and 

 figured Onoha saxatilis Moller, Onoha cerinella 

 Dall, and Onoha aleutica Dall. The first I now 

 rename Nodulus Tcyskensis, since an abundance 

 of saxatilis for comparison force me to declare 

 the Alaskan form distinct. Onoha aleutica Dall 

 ranges nearer the West American species of 

 Cingula, to which it is now referred. 



The only other Nodulus described from the 

 West Coast is Nodulus asser Bartsch, published 

 in the Nautilus ^ for 1910, also from Alaska. 



A fourth species, Nodulus Jcelseyi, is now added 

 from Coronado Island, California. 



NODXJLUS CERINELLUS Dall. 



Onoha cerinella Dall, Proc. U. S. Nat. Mus., vol. 9, 1886, 

 p. 307, pi. 4, fig. 12. 



Shell small, thin, light yellow. The nucleus '^'^^^ 

 consists of a single turn, which is smooth and 

 scarcely difl^erentiated from the succeeding whorls. Post-nuclear 

 whorls high between the sutures, moderately rounded, appressed at 

 the summit, marked by fine incremental lines only. Suture well con- 

 stricted. Periphery of the last whorl and the rather long base gently 



1 Proc. U. S. Nat. Mus., vol. 9, 1886, pp. 306-7. 2 Nautilus, vol. 23, No. 11, p. 138, pi. 11, fig. 9. 



Proceedings U. S. National Museum, Vol. 41— No. 1858. 



289 



