96 SYSTEMATIC ARRANGEMENT 



notch to fit this groove, but this was not the case with our speci- 

 men, and was perhaps an accident in the one described. 



They are amphibious, and are found in shallow pools at the roots 

 of the mangroves, or adhering to stones far inland and exposed to 

 the sun. 



b. Litiopina. " Opercular lobe bearded." — Eydoux. Pelagic, 

 floating. 



3. Litiopa. 



Shell thin, conical ; spire acute ; mouth ovate, nicked in front ; 

 outer lip simple, acute. Operculum horny. Mantle bearded. 



1. L. bombyx, t. 24. f. I, 2. 



2. L. melastoma, t. 107. f. 3, cop. Adams, Gen. Moll. t. 34. f. 5. 



Small animals are found on the Gulf weed, to which they attach 

 themselves by means of a byssus which they secrete. 



The operculum of Litiopa was overlooked by MM. Rang and 

 Kiener. Prof. d'Orbigny {Cuba, 148) states that he observed it in 

 all the specimens given him by M. Rang, so that all the reflections 

 made by M. Rang respecting its absence at once fall to the ground. 

 He also observes that the two species described by the same author 

 are only varieties, occasioned by diiference of age, of the same kind, 

 viz. L. bombyx of Kiener. The shells of the young animals are 

 longitudinally grooved or costated. 



Fam. XIII. RISSOAD.E. 



Rostrum produced, adherent to the front of the foot beneath, 

 Jaws horny. Teeth 3*1*3; outer lateral denticulated. Tentacles 

 setaceous ; eyes sessile, basal, external. Foot short, truncated in 

 front ; opercular mantle rather expanded, often furnished with one 

 or two posterior processes. Operculum horny, spiral. Shell ovate, 

 costated, white, covered with a thin periostraca. Mouth ovate, sim- 

 ple, with a slight canal in front. 



f Operculum ovate, with an internal process on the front edge. 

 Mouth subtruncate in front. 



1. Rissoina. 



Animal ? Operculum semilunar, subspiral ; inner side with 



a longitudinal muscular impression and an elongated process before 

 it as in Nerita. Shell turrited, ribbed or cancellated ; spire pointed ; 

 aperture ovate, effused interiorly, slightly channeled in front ; outer 

 lip dilated anteriorly, thickened internally. 



1. R. Cumingii, Adams, Gen. Moll. t. 35. f. 1 (shell only). 



2. R. Inca, cTOrb. Amer. Merid. t. 53. f. 11-16 (shell only). 



These animals live, affixed to stones on rocks at the common low 

 water line, on the coast of Peru. 





