NERITID-<E. 295 



Distr. — 2 sp. Oligocene and Miocene ; Paris and Bordeaux 

 basins, D. Neritoides, Grrat. (Ixxviii, 59). 



Shell subglobose, thick, umbilicated ; spire sliort ; aperture 

 entire, semicircular, oblique ; columella oblique ; callosity den- 

 ticulated ; umbilicus covered by the callosity ; light lip acute, 

 smooth internally. 



This genus presents a very remarkable combination of the 

 characters of Natica and Nerita, and appears to establish a pas- 

 sage between these two genera, types of distinct families. 



Neritopsis, Grateloup. 



Syri. — Radula, Gray. Peltarion, Desl. Cyclidia, RoUe. Del- 

 phinulopsis (in part), Laube. Scaphanidia, Miill. (The last 

 three founded on opercula.) 



Distr. — 1 recent and 20 fossil sp. Triassic — ; Europe. N. 

 radula, Linn. (Ixxviii, 60-62). 



Shell subglobular, neritiform, with the spire a little elevated ; 

 columellar lip not dentate, largely excavated or sinused in the 

 middle. The fossil opercula of this genus were, until recently, 

 believed to be the beaks of cephalopods (Peltarion). 



Neritoma, Morris. 



Distr. — Jurassic ; Europe. iV. angulata, Sowb. (Ixxviii, 63). 



Shell ventricose, thick ; apex eroded ; aperture with a notch 

 in the middle of the outer lip ; inner lip excavated in the middle, 

 without teeth. Casts of this shell are common, and exhibit the 

 condition of the interior characteristic of all the Nerites ; it was 

 probably fresh water. 



NERiDOMUS, Morris and Lycett. Shell smooth, ovately globose ; 

 spire small, oblique ; the last whorl very large ; apertui^e ovate 

 or semilunar ; outer lip thick, inner lip thick, convex and smooth. 

 Great Oolite; England. N. hemisphcerica, Romer (Ixxviii, 64). 



Neritina, Lam. 



Syn. — Neritella, Humph. Lamprostoma, Swains. 



Distr. — 140 sp. Tropical and subtropical ; West Indies, 

 Europe, India, Philippines, Polynesia, West America. Fossil, 

 20 sp. Jurassic, Eocene — . N. communis, Quoy (Ixxviii, 65). 



Shell globular, rather thin, aperture-margin thickened ; outer 

 lip acute ; inner lip straight, denticulated. Operculum shelly 

 with a flexible border ; exhibiting two processes which von 

 Martens calls the "rib" and "peg," and in which he has found 

 the characteristics of several groups of minor value. Animal 

 similar to Nerita. 



Neritina can only be distinguished from Nerita by slight dif- 

 ferences in the operculum and by the general facies. 



The Neritinse are small, smooth globular shells, ornamented 

 with a great variety of black or purple bands and spots, covered 



