512 
GEOGRAPHICAL ZOOLOGY. 
[part IV. 
Family 20. — DENTALIADAL (1 Genus, 50 Species). 
Distribution. — The genus Dentaliicm is found in the North 
Atlantic, Mediterranean, West Indies and India. There are 
125 fossil species, found in various formations as far back as 
the Devonian in Europe and in Chili. 
Family 21.-— CHITONIDJL (1 Genus, 250 Species). 
Distribution. — On rocky shores in all parts of the world. 
There are 37 fossil species ranging back to the Silurian 
period. 
Order II . — P UL M ON II ERA . (“ Terrestrial Molluscs.”) 
The Land and Fresli-water snails are so important and exten- 
sive a group, and their classification has been so carefully 
studied, that their geographical distribution is a subject of much 
interest. The range of the genera will therefore be given in 
some detail. For the Helicidse I follow the classical work of 
fibers — Di 6 Helicien, Yon Martens’ Edition (1860) ; and for 
the Operculate 1 families, Pfeiffer’s Monographia Fneumonopo- 
morum Viventium , 2nd Supplement, 1865. The number of 
species is, of course, very considerably increased since these 
works were published (and the probable amount of the increase 
I have in most cases indicated), but this does not materially 
affect the great features of their geographical distribution. 
Family 22.— HELICID^. (33 Genera, 3,332 Species) (1860). 
General Distribution, — Universal. 
The Helicidse, or Snails, are a group [of immense extent and 
absolutely cosmopolitan in their range, being found in the most 
barren deserts and on the smallest islands, all over the globe. 
They reach to near the line of perpetual snow on mountains, and 
