524 



MOLLUSCA 



PHYLÜM VI 



nally. OiUer lip ivith a sUt, from which a slit-hand {the anal fasciole) extends hackward, 

 traversing all the whorls. The slit sometimes replaced by one or more perforations. 

 Operculum horny. Cambrian to Kecent. 



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

 sometimes high, in other cases depressed ; umbilicus present or absent. Guter lip 

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

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

 Tertiary. 



Subgenera : Ptychomphalus Agassiz ; Mourlonia, Worthenia, Agnesia de Koninck ; 

 Gosseletina, Ivania {Baylea de Kon.) Bayle ; Raphistoinella (Fig. 851, A), Zygites, Laubella, 



Fig. 852. 



A, PZetwoiomaria iyifor^uato Deslongchanips. Middle Lias ; May, Calvados. B, P. suhscalaris 

 Deslongchamps. Lower Oolite ; Bayeux, Calvados. 1/2- 



Fig. 853. 

 Pleurotomaria {Leptoinaria) mojcrompTialla Zittel. 



Tithonian ; Stramberg, Moravia. 



Stuorella, ScMzodiscus Kittl ; Brüonella Kayser ; Hesperiella Holzapfel ; Cryptaenia (Fig. 

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



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

 discoidal, flat, widely iimbilicate, 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. 



Kohenella Kittl. Very flat, discoidal, and only slightly 

 asymmetrical, with a broad slit-band. Trias. K, 

 (Hoernes). 



Fig. 854. 



Car- 



Porcellia puzosi Leveille. ^ 



boniferous ; Tournay, Belgium 



