280 Zoological Society. 



Inferior surface less flat, pale rosy brown or reddish brown, as well 

 as the teeth, which offer nothing particular, and which resemble 

 those of the opercula of Ner. pulligera and other allied species. The 

 operculum of var. (j is of an uniform colour above, on account of 

 its zones being confluent. That of var. y is of a very pale green, 

 with a circular stria, which divides its external surface in two parts 

 almost longitudinally. This character is also observable upon the 

 operculum of var. /3, but very faintly. There is no trace of it upon 

 the type. 



* * * Spinosse, interdum muticoe (Clithon, Montfort). 



11. Nerita oLivACEA. N. testd ovato-glohosd, ventricosd, crassd, 

 griseo-olivaced, anfractihus 2^, superrie depress'msculis ; apice sub- 

 convexo, obtuso, latei^ali, in medio deroso ; aperturd extus subqua- 

 dratd, inths exalbidd, labia postice rufescente, plana, margine 

 crenato, et in media vix arcuato. 



Long. M2 ; lat. 1*36 ; conv. 0-76 poll. 



Hab. Agoo, province of Pangasinan, island of Lu9on : on stones 

 in a rapid river. ' 



This Clithon has sometimes a brownish zone posteriorly, with some 

 faint reddish spots. The summit of the shell is corroded and exca- 

 vated. Operculum of a Clithon, rosy white, spotted with red at the 

 summit, and faintly marked with a circular streak in the centre of 

 its external surface. The interior surface is reddish, convex, and 

 flattened at the base ; two teeth at the top, the upper one lamellated, 

 elevated into an obtuse point ; the second or inferior one circular 

 and striated. Underneath this tooth there is a great depression. 



12. Nerita bicolor. N. testd ventricoso-ovatd, crassiusculd, sub 

 suturd depressiusculd, strigis nigris et olivaceis longitudinalibus 

 dense pictd; apice eroso; aperturd extiis subquadratd exalbidd; labia 

 plana, superne callasa basi canaliculata, margine in media arcuato, 

 et obsolete dentata ; dente cardinali majori. 



Long. 1-04; lat. 1-20; conv. 0*76 poll. 



Hab. Agoo : in a mountain-stream. 



Operculum of a Clithon, oval, solid, whitish, striated lengthwise 

 in an oblique direction, and marked with a circular furrow from the 

 summit to the posterior margin, ending in a slight notch ; inferior 

 surface furnished with a large, circular, slightly raised rib, prolonged 

 in an obtuse angle at the posterior margin. Two teeth at the top : 

 the upper one an oblique rosy plate terminated at the summit ; the 

 lower one circular, delicate yellow, enlarged at the summit, and 

 striated lengthwise and across. 



13. Nerita interrupta. N. testd ovato-semiglabosd, apice valdh 

 corrosd et truncatd, olivaced, linealis luteis interdum interruptis 

 creberrimis et fasciis latiusculis luteis transversis pictd; aperturd 

 extiis semi'Ovali, intus luted ; labia subsemilunari, plano-concavq, 

 margine in media arcuato, acuta, dente cardinali exserto. 



Lat. 0-96 ; conv. 0*64 poll. 



Hab. Yba, province of Zambales, isle of Lu9on : on stones in a 

 rapid river. 



