113 



compressed in the left outline : labial deposit rather thick ; umbili- 

 cal callus nearly filling the rather narrow umbilicus. 



Mean divergence about 120°; length of aperture .42 inch; total 

 length .53 inch ; breadth .43 inch. 



Variety nigrescens is more concave around the umbilicus, is rather 

 larger and thicker, and has the callus and interior of the aperture 

 nearly or quite black. 



Neritina ornata. Shell obliquely ellipsoidal : rather pale green- 

 ish or livid brown, ornamented with numerous rather small irregular 

 spots of bright red : rather thick and solid, with fine unequal striae 

 of growth, and crowded microscopic spiral lines: spire small, not 

 very prominent: whorls more than three, with a subcanaliculate su- 

 ture : labium smooth, obsoletely toothed. Operculum divided into 

 two concave regions by an acute ridge, which is curved in the direc- 

 tion of growth. 



Length of spire .07 inch ; total length .32 inch ; breadth .24 inch. 



Neritina (?) pusilla. Shell transversely ovate : white, translu- 

 cent : vitreous, smooth and shining : spire scarcely elevated : whorls 

 one and one-half, with an indistinct suture; last whorl very large, 

 concavely depressed above : aperture very large, semiorbicular : la- 

 brum very thin : labium tumid, covered wilh a large tumid smooth 

 deposit. Obviously this species can scarcely be included in Neritina. 

 A considerable number of specimens were obtained, which scarcely 

 differ even in size. 



Height .04 inch ; greatest breadth .068 inch. 



Like most of the Neritinae of Jamaica, this is strictly a marine 

 shell. 



Two or three of the following species of Rissoa may have been 

 described by Orbigny in the Moll, du Cuba, but not having the text 

 we are unable positively to identify them, and therefore offer the fol- 

 lowing preliminary description of all the species from Jamaica, which 

 were not described in the Proc. Bost. Soc. Nat. Hist., Jan., 1845. 



The same remark may be true of one or two species of Chemnitzia 

 on pp. 72- 5. 



Rissoa subanoulata. Shell long ovate conic: white: with, on 

 each whorl, eleven or twelve rather acute but stout ribs, which spread 

 to their bases with concave sides, and which on the last whorl are 

 produced to the anterior extremity ; sometimes with very lightly ira- 



