524 



MOLLUSCA 



PHYLUM VI 



nally. Outer lip with a slit, from which a slit-hand {the anal fasciole) extends bachvard, 

 traversing all the ivhorls. Tlie slit sometimes replaced hy one or more perforations. 

 Operculum horny. Cambrian to Eecent. 



Pleurotomaria Sowb. (Figs. 851-853). Shell broadly conical or turbinate; spire 

 sometimes liigli, in other cases depressed ; nmbilicus present or absent. Outer lip 

 with slit ; growth-lines strongly recurved, meeting in the slit-band. Silurian to 

 Recent. Four living and several hundred fossil species known. Rare in the late 

 Tertiary. 



Subgenera : Ptycliom]}halus Agassiz ; Alourlonia, Worthcnia, Aynesia de Koninck ; 

 Gosscletina, Ivania (Baylea de Kon.) Bayle ; Baphistomella (Fig. 851, A), Zygitcs, Laubclla, 



Piu. S52. 



A, Pleurotomaria ftitorguaia Deslongchamps. Middle Lias ; May, Calvados. B, F. suhscalaris 

 Deslongchamps. Lower Oolite ; Bayeux, Calvados, i/o. 



Fig. 863. 

 l'U:urotomaria(Lc2itomaria)macroin2)lialla Zittel. Tithonian ; Stramberg, Moravia. 



Stuorella, Schizodiscus Kittl ; Brilunella Kayser ; Hespericlla Holzapfel ; Cryptacnia (Fig, 



851, B), Leptomaria Deslongchamps (Fig. 853), etc. 



Porcellia Leveille (Leveilleia Newton) (Fig. 854). Shell 

 discoidal, flat, widely umbilicate, nearly symmetrical, and 

 all but the first few whorls coiled in the same plane. Outer 

 lip sharp, with long slit. Slit-band prominent, traversing 

 the central portion of the whorls. Devonian and Carboni- 

 ferous. 

 Pjj, gr;^ Kohenella Kittl. Very flat, discoidal, and only slightly 



PorceHiapwmsi LevoiUe. Car- asymmetrical, with a broad slit -band. Trias. K. fischeri 

 boniferous ; Tournay, Belgium. (Hoernes). 



