GASTEROPODA. 



135 



fissure, Operc. with a broad, membrauous border, W. Indies, Zanzibar, 

 Pacific. 



Modulus, Gray (and nina, Gray) M, tectum, PI. IX., fig. 13. Shell tro- 

 chiform or naticoid ; porceUanous ; columella perforated ; inner lip worn or 

 toothed ; operc. horny, many-whirled. Distr., Philippines, W, America. 



Fossarus (Adans.) Philippi. F. sulcatus, PI. IX., fig. 12. Syn., pha- 

 sianema. Wood. SheD perforated ; inner lip thin; operc. not spiral. Distr., 

 Medit. Foss-il, 3 sp. Miocene — . Brit., Medit. 



Risella, Gray. Lit., melanostoma, PI. IX., fig. 14. Shell trochiform, 

 with a flat or concave base ; whirls keeled ; aperture rhombic, dark or vaj-ie- 

 gated, operc. pauci-spiral. Distr., N. Zealand. 



Solarium, Lam. Stair-case shell. 



Eti/m., solarium, a dial. 



Syn,, architectoma, Bolten. Philippia, Gray. HeHcocryptus, D'Orb ? 



Tyj)e., S. perspectivum, PI. IX., fig. 15. 



Shell orbicular, depressed ; umbilicus wide and deep ; aperture rhombic ; 

 peristome thin ; operculum horny, sub-spiral. 



The spiral edges of the whirls, seen in the umbilicus, have been fancifully 

 compared to a winding stair-case. 



Distr., 25 sp. Tropical seas. Medit., E. Africa, India, China, Japan, 

 Australia, Pacific, W. America. 



Fossil, 56 sp. Eocene—. Brit., &c. 26 other sp. (oolites— chalk,) are 

 l)ro\-isiouaIly referred to this genus ; the cretaceous sp. are nacreous (v. 

 trochus) . 



Sub-genera. Torinia, Gray. T. cylindracea, operc. conical, 

 multi-spiral, with projecting edges, fig. 82. Living, New Ire- 

 land. Fossil, Eocene. Brit. Paris. 



Omala.vis, Desh, (altered to bifrontia) S. bifi'ons, discoidal, 

 the last whirl disengaged. 6 sp. Eocene, Paris, Brit. 



? Orbis, Lea. Discoidal, whirls quadrate. Fossil, Eocene, 

 America. 



? Phorus, Montf. Carrier-shell. 



Eti/m., phorev.s, a carrier. 



Si/ii., onustus, Humph., Xenophorus, Fischer. 



Examples, P. conchy liophorus, Born. P. corrugatus, PI. X., fig. 1. 



Shell trocliiform, concave beneath ; whirls flat, wdth foliaceous 

 or stellated margins, to which shells, stones, &c., are usually 

 affixed ; apertm-e very oblique, not pearly ; outer lip thin, much 

 produced above, receding far beneath. Operc. horny, imbricated, 

 nucleus external (as yq. imrfura and paludomus,) wdth the trans- 

 verse scar seen tlu-ough it, fig. 83. (Mus. Cuming.) 



* Operculum of S. patulum, Lam. ^, from Desliayes. 



Fig. 83. 



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