GASTEROPODA 77 



Loxonema (fig. 17, i), and Macrochilus (fig. 17, 2). The violet- 

 snail (Ianthina), so unlike any other existing shell-fish, seems 

 related to the Silurian Scalitcs, RcqMstoma, and Holopea. 

 Shells like Scalaria and Solarium occur in the trias and oolites 

 associated with Clicmnitzice (V) of extraordinary size, and species 

 of Eulima and Kiso. These families of shells and the Ceri- 

 thiadce are more abundant fossil than recent, the known num- 

 bers being 1500 extinct and 900 living forms. Solaria, with 

 disconnected whirls and pyramidal opercula (Bifrontia, Dh.), 

 are common in the eocene tertiary, and a single living species 

 (B. za?iclcea) has been discovered by M' Andrew. 



Amongst the tertiary Naticas are many with an oblique 

 aperture and peculiar perforation {Globulus, J. Sby., = Am/pul- 

 lina, BL), and others w T ith prominences on the pillar (Dcshayc- 

 sia, fig. 19, 6.) The Nerinceasoi the oolites are remarkable for 

 the spiral ridges (like the " worm" of a screw T ) winding round 

 their interior, and giving rise to the variety of singular pat- 

 terns seen in sections (fig. 18,4). A similar structure exists 

 in the recent " telescope-shell" (TcrcbraliaS. The fresh-water 

 univalves of the "Wealden and older tertiaries differ but little 

 from their recent congeners of the genera Paludina, Potamidcs, 

 Mclania, and Mclanojms. Fossil Tvrritdlcc are of doubtful 

 occurrence before the tertiary ; the Silurian species have the 

 peristome complete (Holqpella, M'C); another form (Proto, 

 fig. 19, 7) is characteristic of the miocene. 



The bonnet-limpets (Calyptrceidw) are common in the old 

 rocks, which also contain a few species of Chiton and shells 

 like Dentalium. Fossil Trochidcv are very numerous, but 

 hitherto many Litorinidw have doubtless been included with 

 them. Perhaps no true Turbo is known from strata before the 

 cretaceous. The Euompliali (fig. 17, 4), which characterize the 

 older rocks, have multispiral calcareous opercula, like the 

 recent Cyclostrema ( -— Adcorbis). The genus Ma civ. ir a (fig. 

 17. 9), which has been regarded as a "left-handed" Euompha- 



