MANUAL OF THE MOLLUSCA. 
surface smooth or but slightly 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 Plewrotomaria 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, Fischer, 1861. 
Type, S. striatuia, Ph. Mediterranean. 
Shell like Scissurella, but the. spire is laterally compressed, as 
in Stomatia, and is not so trochiform. Theslitin 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 Trochotoma, differing only in size; but in the 
two former genera the shell is translucent, not nacreous, as in 
the two latter. 
DITREMARIA* (pars, D’Orb.), E. Deslongchamps, 1865. 
Fig. 15. Ditremaria quinguecincta. 
a, Central tooth. 6, Callosity of the base. c, Tooth on the right. d, Tooth on the left. 
Type, D. quinquecincta, Ziet. sp. Coral Rag. Natheim, &c. 
Shell trochiform ; in place of the respiratory slit of T'rocho- 
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. 
38 
