214 LECTURES ON MOLLUSCA. 



of the pillar scooped out, and the lip ornamented with blunt teeth. 

 When these become obsolete, with sharply keeled whirls, the shell 

 resembles Trochita among the Slipper-limpets, and is called Infundi- 

 bulum. 



The Australian and New Zealand Top-shells present some curiously 

 drawn-out forms ; in which the nacre has generally a greenish hue. The 

 shell of Caniharis has a plain pillar, like Pliasianella. In Elenchus, 

 which is polished and painted like the Pheasant-snails, there is a tooth 

 on the pillar ; and in Thalotia the mouth is toothed round. Banhivia 

 is a curious j^wfo'ma-shaped shell, with the pillar bent and truncated. 

 Although it is so common as to be used for ornaments by the natives, 

 its operculum and animal are still unknown. 



In the next group the shape of the shell is more ovate, with flat- 

 tened spire and rounded base. Livona has convex whirls and a round 

 mouth, with a deeply-pierced pillar and lump bordering the hole. 

 The L. pica is one of the most characteristic shells of the West Indies : 

 a closely allied form was taken alive by Colonel Jewett in California. 

 The operculum has fewer whirls than is usual in the tribe. TrocMs- 

 cus, a form peculiar to California, is nearly allied, but has the oper- 

 culum with raised and scaly edges. In Gibbula, a very common Euro- 

 pean form, the whirls are shouldered, and the pillar-lip is plain. 

 Margarita is a closely allied boreal group, with very thin shells and 

 round mouth. The very similar forms Oxy stele and Diloma are like a 

 Livona with a closed pillar. 



The shells of Clanculus are remarkable for their ringent mouths, 

 twisted by numerous teeth. Monodonta is shaped like a Periwinkle, 

 with one stout tooth on the pillar, and others round. Euchelus differs 

 from it in being umbilicated, with but few whirls in the operculum. 

 Osilinus is like Monodonta, with only one plain knob on the pillar. 

 Omjjhalius, the shells of which replace Gibbula on the west coast of 

 America, is like a plain Clanculus, with the pillar lip toothed, some- 

 what as in Modulus. Tegula, which is peculiar to the Panama region, 

 has the mouth of Osilinus, with the Trochoid shape of Omphalius. 



Monilea is a little group of sculptured shells, resembling Torinia, in 

 which the open pillar is bounded by an ornamented spiral ridge. 



The Delphinida group are in shape like strong, shaggy sea Cyclosto- 

 mas. The pillar is quite open ; the whirls scarcely touch ; and the 

 mouth is round. 



Several fossil forms appear allied to this and other recent genera ; 

 but in ignorance of their opercula, we cannot locate them with cer- 

 tainty. EuomjjJialus is like a flat, thin, unsculptured DelpMnula, with 

 angular mouth. The typical species of Cirrus are so irregular that 

 they might be considered Vermetids. The C. nodosus of the English 

 Oolites, sometimes begins as a left-handed Turritella, ending in a flat 

 Euomphalus ; and sometimes take a reversed top-shape from the be- 

 ginning. In some species, the whirls are disunited. Some species of 

 Euomplialus are believed to have had a stony operculum like Turbo. 



Family Liotid/^. 

 Some of the shells classed with Delphinida are found to have the 



