PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 343 



Ptipilla decora Gould. 



r. decora Gld. Proc. Bost. Soc. Nat. Hist., ii, p. 263, Dec, 1847. 

 P. borealis Morelet. J. de Conchyl., vii, p. 9, July, 1858. 



Found at Bering Island. Collectors' numbers 1051, 1514, and 1517, 

 Mus. Cat. 40914. Dr. Eeinhardt identifies this, which is certainly 

 borealis MoR., with Gould's prior P. decora. 



Limnaea ovata Draparnaud. 



L. ovatus Drap. Hist, des Moll, terr., p. 50, pi. ii, figs. 30, 31. 1805. L. ampla 



MiGHELS. 



It is to this form rather than to auricularia that the L. ampla of 

 Mighels is related. From the polished globose, transversely striate, 

 rather loosely rolled, and umbilicated specimens obtained September 2 

 from Lake Saramraja, on Bering Island, by Dr. Stejneger, the Aleutian 

 form L. var. atJcaensis Dall difters in being more compact, less polished, 

 with a taller spire, more turreted and less rounded whorls, the coarse 

 malleation of nearly all the specimens, which are also a little more solid 

 and have only a chink in the umbilical lilace. From ovata, atkaensis 

 leads to sumassi Baird and ampla Mighels. A large series shows a 

 l^retty gradual transition so far as the shells are concerned. Collector's 

 number, 1502. Mus. Cat. 40915. 

 Limndea humilis Say. 



Specimens which are provisionally referred to the above species were 

 found in a pond near Ladiginsk with Pisidium cequilaterale Prime, 

 July 22, Bering Island. I have no doubt it is common to Eastern Siberia, 

 and it may be identical with Westerland's L. tnmcatnla var. microstoma 

 Drouet, but at present I am unable to compare specimens. Collector's 

 number, 1267. Mus. Cat. 40916. 



The absence of Succinea and Cocfilicopa, not to mention Aplexa liyp- 

 nornm, from these isolated isles is almost as noteworthy as the existence 

 there of large Limnaeas. Why Patiila striatella should be absent when 

 other similar species occur is one of the problems for which we can 

 offer no solution. 



GASTKOPODA. 



(Marine.) 

 Placophora. 



Trachyradsia aleutica Dall. 



Bering Island, rather common. Collector's number, 1497. Mus. Cat. 

 40917. This species was first described from the western Aleutian Isl- 

 ands, and has not yet been reported from either continent. 



Tonicella marmorea Fabricius. 



A single specimen from Bering Island. Collector's number, 2362. 

 Mus. Cat. 40918. 



