146 Zoological Society. 



teriorly, with a projecting, obtuse, linear tooth, which is divided by 

 a shghtly impressed longitudinal groove ; the right margin very nar- 

 row, very thin, and without crest. 



It is possible that this species may prove only a stronger, more 

 robust state of the Nav. tessellata ; nevertheless it differs in its gene- 

 ral form, and its operculum also shows some differential characters. 



7. Navicella tessellata, Lamarck. 



Var. a. T. lateribus angustatd, suhrectis ; sub epidermide lutescente 

 lineolis violaceis sen piirpureis creherrimis, et maculis conicis con- 

 centrice seriatis pictd ; vertice recto, luteo ; labia triangulari, antice 

 subarcuato, lateribus prolongato. 

 Var. (i. T. ut in var. a, sed postice subemarginatd, griseo-fuscd, 

 maculis minoribus luteo -fuscescentibus conicis crebre pictd; apice 

 dilute purpuras eente, recto ; labio subtriangulari, angusto, roseo, 

 antice arcuato. 

 Var. y. ? T. oblongo-ellipticd, antic^ et postice rotundatd, crassiore 

 sive oblongo-acutd, lateribus angustatd, nigcrrimd, apice eroso ; 

 labio semilunari, interdum triangulari, latiore, subrecto, lateribus 

 non prolongatis. 

 An Nav. Clypeolum, var. ? credo, sed difficile est probandi sine 

 operculo. 



Long. 0-80 ad 0-92 ; lat. 0-76 ad 0*92 ; conv. 0*24 ad 0-48 poll. 

 Hab. Var. a, Cagayan : found in a large river on stones. Var. /3, 

 from Baccara, province of North Ylocos, island of Lu^on : found on 

 stones in a placid river. Var. y. ? , from Abulug, province of Cagayan, 

 island of Lu^on : found on stones in a large river. 



Operculum square, a little elongated, naiTow, and cut almost 

 square anteriorly, with a slight notch towards the apophysis, which 

 is slightly curved inwards (instead of being straight or turned back- 

 wards, as in that of Nav. clypeolum). The inclined angle of the 

 middle of the left side is deeper, and in this species shows a depres- 

 sion or broad canal, in form of a A, the whole length of the apophy- 

 sis ; this canal is limited to the left by two slightly raised ribs. 



These characters of the operculum, if they be constant, should 

 suffice to avoid all confusion of this species and the one which pre- 

 cedes. 



8. Navicella lineata, Lamarck. 



Var. a. T. oblong d, postice acuta, luteo-aured, superne lineis spa- 

 diceis radiantibus ex lineolis transversis obumbratis, antice et laie- 

 raliter maculis oblongo-conicis subserialibus pictd ; apice lateraliter 

 compresso, supra fornicato, I'oseo-purpurascente recto, marginali ; 

 labio angusto-triangulari, medio concavo-emarginato, lateribus an- 

 tice prolongatis. 



Var. /3. T. ellipticd, postic^ angustatd, luted medio dor si lineis ni- 

 gris angustis et latiusculis, et lineolis obliquis creberrimis radiis 

 latioribus lateraliter efformantibus interdum confiuentibus pictd, 

 labio triangulari antice arcuato. 



Var. y. T. oblongd, postice angustd, subacutd, luted radiis angustis 

 nigris medio dorsi notatd, antic^ et lateraliter crebre nigrescente 



