280 PLANAXIS. 



This appears to be an undoubted inhabitant of fresh water, and 

 as such is an interesting novelty ; but are not its affinities with 

 Melanopsis rather than with Planaxis ? 



Subgenus Quoyia, Desh., 1830. 

 P. decollatus, Quoy. PI. 53, figs. 71, 70. 



Strongly spirally grooved, grooves stronger on the base ; colum- 

 ellar lip excised above; epidermis olivaceous, with dull chestnut 

 obliquely longitudinal strigations ; apex decollated. 



Length, 28 mill. 



Philippines, Ascension IsL, Netv Guinea. 



It is Monoptygma melanoides, Lea, and P. Michaui, Crosse and 

 Fischer (fig. 70.) The latter is founded on a younger specimen, in 

 which a chestnut peripheral band appears, and the interior of the 

 outer lip is not ridged ; both these characters merge into the normal 

 type of the species with increasing age. 



Subgenus Holcostoma, H. & A. Ad., 1853. 

 P. piLKJERUs, Phil. PI. 53, figs. 62, 69. 



Smooth, under a bristly epidermis, yellowish brown, with two 

 chestnut bands, outer lip dentate within. Length, 8 mill. 



Mauritiics. 



The first figure is from an adult denuded of epidermal hairs, the 

 second represents H. setir/eram, A. Ad. (fig. 69), which is said by 

 Mr. E. A. Smith, of the British Museum, to be identical ; if so, it 

 must be a much-magnified figure of a young shell wliich has not 

 yet acquired the teeth to the outer lip. 



Unfigured Species of Planaxis. 



P. iNCisus and P. t^eniatus, Phil. Hah. unknown. 



P. NUCLEOLA, Morch. West Indies. 



P. BUCCINEA, A. Ad. West Indies. 



P. GouLDi, Smith (P. cingulatus, Gld., not Ads.) Japan. 



P. AKEOLATus, Lcsson. Tahiti. 



P. SEMiL^vis, Martens. Socotra. 



P. EBENINUS, Menke. Peru. 

 Subfamily Litiopin^, 

 Genus LITIOPA, Rang., 1829. 

 L. MELANOSTOMA, Rang. PI. 53, figs. 72-75, 78. 



Whorls about 9, slightly convex, towards the apex microscopi- 

 cally longitudinally costulate, other whorls very finely spirally stri- 



