2 LITTORINID.E. 



In a valuable paper by M. Morch, " On the Homo- 

 logy of the Buccal Parts of the Mollusca " (Ann. and 

 Mag. N. H., August 1865), the cheek-plates or immo- 

 veable mandibles of this and other genera are described 

 as two lateral plates, without cutting-edges, composed 

 of scaly or needle-shaped particles, which seem only of 

 use to protect the inside of the mouth from being in- 

 jured by the spinous tongue. The opercular appendage 

 was first noticed by Bivona. It seems strange that 

 Philippi could not detect it, and that notwithstanding 

 he had figured seven species (including Barleeia rubra) 

 he should have remarked, " Hse species omnes simillimis 

 animalibus incoluntur." The pallial filament protrudes 

 at the will of the animal from the upper or anal corner 

 of the aperture of the shell. Hydrobia and Odostomia 

 have similar processes. In Rissoa striatula and R. can- 

 cellata there are two, one on each side. These, there- 

 fore, are certainly not organs of generation. The fila- 

 ment is found in every individual ; and all the above- 

 named genera are dioecious or unisexual. It may be an 

 auxiliary tentacle. The spawn-cases are solitary and 

 hemispherical. 



The ' Transactions of the Imperial Academy of Sci- 

 ences at Vienna' for 1863 contain an elaborate and 

 admirably illustrated monograph by Gustav Schwartz 

 v. Mohrenstern of part of this difficult group ; I hope 

 the remaining portion will soon be published. He has 

 provisionally adopted the views of Messrs. H. and A. 

 Adams to the extent of considering Alvania a distinct 

 genus ; but his reason for so doing seems to have origi- 

 nated in a misapprehension. According to the learned 

 Austrian conchologist, Alvania is distinguished from 

 Rissoa by having three caudal filaments instead of one. 

 The authors of the ( Genera of recent Mollusca ' say as 



