4 REPORT 1856. 



Fig. 4. Coecum undatum, magnified, exhibiting development and variations in shape, 

 sculpture, form of mouth, prominence of plug, &c, observed among about 

 340 specimens. Similar changes in the common Panama species form the 

 C(Bcum diminutum, C. pygmceum, C. monstrosum, C. eburneum and C.fir- 

 matum of Prof. C. B. Adams : (a, young Ccecum, with spiral part attached, 

 species not known ;) b, tube smooth and short ; c, ditto, long ; d, with 

 faint indications of rings near the margin ; e, shell more curved ; marginal 

 rings stronger;/, shell passing at once from smooth to fully ringed state; 

 g, the same, more bent, rings irregular ; h, ditto, curvature irregular ; 

 i, with more rings, outline very irregular ; j, stumpy form, rings close, 

 mouth immature ; k, adult, front view, with multispiral operculum in situ, 

 apical portion smooth ; I, another specimen, mouth contracted, apical 

 portion ringed; m, normal state, profile; n, specimen with rings almost 

 evanescent ; o, deformed specimen, broken, and mended without rings. 

 All the irregularities in these figures are intended. 



Fig. 5. Neritina cassiculum, Sby. : a, elevated state, corresponding with subgenus 

 Vitta (Klein) of Messrs. Adams; b, normal state, subgenus Neritina 

 (Swains.) of Messrs. Adams ; c, depressed state, answering to restricted 

 genus Neritella (Humph.) of Messrs. Adams. The same changes of form 

 are observable in the very closely related Neritina picta, Sby. = Vitta 

 picta of Messrs. Adams. 



P. P. Carpenter. 



