280 Zoological Society. 



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

 as the teeth, which ofter noticing particular, and which resemble 

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

 operculum of var. /3 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. /5, but very faintly. There is no trace of it upon 

 the type. 



* * * Spinosse, interdum rauticse {Clithon, Montfort). 



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

 griseo-oUvaced, anfractibus 2^, supeime depressiuscuUs ; apice sub- 

 convexo, obtuso, laterali, in medio deroso ; aperturd extiis subqua- 

 dratd, intus exalbidd, labio postice rufescente, piano, margine 

 crenato, et in medio vix arcuato. 



Long. 1-12 ; lat. 1-36; conv. 0-76 poll. 



Hab. Agoo, province of Pangasinan, island of Lu^on : on stones 

 in a rapid river. 



This Clithon has sometimes a brovpnish 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; labio 

 piano, superne calloso basi canaliculato, margine in medio arcuato, 

 et obsolete dentato ; dente cardinali majori. 



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



Hub. Agoo : in a mountain-stream. 



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

 in an obhque 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-semiglobosd, apice valdi 

 corrosd et truncatd, olivaced, lineolis litteis interdum interruptis 

 creberrimis et fasciis latiuscuUs luteis trans versis pictd ; aperturd 

 extiis semi-ovali, intiis luted ; labio subsemilunari, plano-concavo, 

 margine in medio arcuato, acuto, dente cardinali exserto. 



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



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

 rapid river. 



