THE NAUTILUS. 23 



Desidiosa, then, differs from obri/ssa {desidiosa of authors) in its 

 generally larger and more solid shell, longer and more turreted 

 spire, more pronounced and heavier sculpture and more convex 

 whorls, with deeper sutures ; in having an internal rib inside the 

 outer lip and in the presence of a fold on the columella. Compared 

 with palustris, desidiosa is smaller, usually more solid and with a 

 more obese body whorl and a more dilated aperture. The spire, too, 

 is more sharply conic and the whorls are more tightly coiled, pro- 

 ducing a deeper suture. The inner lip is also more expanded, 

 producing a heavier callus. The shells called elodes by Say are 

 larger, more flat-sided, with a longer spire, and the whorls are not 

 so rounded and are more oblique. 



If we accept the evidence afforded by Say's specimens (and there 

 seems to the writer to be no other course), then the shells usually 

 called desidiosa must bear the name of ohmssa, which is the first 

 available name, and desidiosa must be used for the shells so-called 

 by Say. 



Explanation of Plate III.' 



Fig. 1. Lymnsea desidiosa Say, Williamsville, Erie Co., N. Y. 

 (from collection of Miss Mary Walker, Buffalo, N. Y.) 



Fig. 2. Say's figures of Lymnsea desidiosa in Amer. Conch., pi. 

 55, fig. 3. 



NOSTHERN 0PI8TH0BRANCHIATA. 



BY F. M. MACFARLAND. 



Northern and Arctic Invertebrates in the Collection 

 OF THE Svtedish State Museum (Riksmuseum). III. Opis- 

 thobranchia and Pteropoda. By Nils Odliner (Kungl. Svenska 

 Vetenskaps Akademiens Handiingar, Band 41, No. 4, pp. 1-118, pi. 

 I-III, 1907). 



The above work will be welcomed by American zoologists as a 

 valuable contribution to our knowledge not only of the Opistho- 

 branch fauna of Scandinavian waters, but also as of great conveni- 

 ence in studying the quite similar fauna of our own North Atlantic 

 shores. The classic Index Molluscorum Scandinaviee of Loven, 1846, 

 and the MoUusca Regionis Norvegise of Sars, 1878, have been for 



' Plate III will appear in the July number. 



