MANUAL OF THE MOLLUSCA. 



surface smooth or but sligMly ornamented, slit excessively 

 short, sometimes reduced to a simple fold ; the band occupies 

 the middle of the whorl, and is only visible on the body whorl. 



Distribution. The species are numerous in the Carboniferous 

 system, and range to the Middle Lias. 



In the typical Pleurotomaria the slit is large, and the band 

 is never concealed by the whorls of the spire. 



SCHISMOPE, Jeffreys, 1856. 



Etymology, schisme, a slit, and ope, a hole. 



Synonym, Woodwardia, Pischer, 1861. 



Type, S. striatula. Ph. Mediterranean. 



Shell like Scissurella, but the spire is laterally compressed, as 

 in Stomatia, and is not so trochiform. The slit in the peristome 

 of the young shell is converted into a foramen in the adult ; it 

 does not commence until the animal is half grown. 



S. striatula is a littoral species, whilst all the species of Scis- 

 surella inhabit deep water. 



Fossil, 1 species, Miocene, Bordeaux. 



Distribution, 4 species. Mediterranean, Japan. 



Scissurella and Schismope are the analogues respectively to 

 Pleurotomaria and TrocJiotoma, differing only in size ; but in the 

 two former genera the shell is translucent, not nacreous, as in 

 the two latter. 



DiTREMAEiA* (pars, D'Orb.), T. Deslongchamps, 1865. 



Fig. 15. Ditremaria quinquecmcta. 

 a. Central tooth. &, Callosity of the base, c, Tooth on the right, d, Tooth on the left. 



Type, D. quinquecincta, Ziet. sp. Coral Eag. Natheim, &c. 



Shell trochiform ; in place of the respiratory slit of Trocho- 

 toma, there are two elongated oval holes united by a transverse 

 fissure ; the base of the shell presents a large callosity, the 

 umbilicus is deeply excavated, and a rounded tubercle arises 



* See p. 271. 



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