728 



A. E. Verrill — The Bermuda Islands. 



shores or around the borders of brackish swamps, belonging to 

 Alexia; Pedipes, 2 sp., fig. 66; Plecotrema; Melampus, 5 sp. ; Trunca- 

 tella, 3 sp. ; Onchidium. These last were probably introduced by 

 natural means. Of the truly terrestrial species there are 4 slugs and 

 23 snails. Among the snails there is a single endemic genus (Pceci- 

 lozoiiites*), with three living and four fossil species, of which three 



69 



i;x 



67a 



676 



Figures 6 7«, 67&. — Pcecilozonites circumfirmatus; x2^. Figures 68, a, 6. — Thy- 

 sanophora hypolepta ; x 10. Figure 69. — Helicina convexa ; x 2. 67, 69, by 

 A. H. V. ; 68, by Pilsbry. 



are extinct. (See Part IV.) Two other species of snails are also 

 supposed to be endemic, viz., Thysanophora hypolepta Pilsb. (fig. 

 68), and Helicina convexa Pfr. (fig. 69), but these are closely allied 

 to West Indian forms. The large slug ( Veronicella Schirelyce 

 Pilsb., fig. 84), known only from Bermuda, in its habits and local- 

 ized distribution appears like an introduced species, but if so its 

 origin is still unknown. 



The following native species of West Indian origin are supposed 

 to have been introduced independently of human agency : 



Thysanophora vortex (Pfr.); Greater Antilles; Bahamas; South- 

 ern Florida. Figs. 70, a, b. 



* This genus is the most interesting one. Its largest species (P. Xelsoni) is 

 extinct, but it occurs abundantly in the older cave-conglomerates and aeolian 

 limestones, sometimes in strata exposed only at low tide, thus showing that it 

 lived on the islands before their partial submergence, and indicating the com- 

 paratively great antiquity of the genus. Its nearest allies are now found in the 

 eastern United States. The three living species are P. Bermudensis ; P. Reinia- 

 nus ; P. circumfirmatus (fig. 67a, 67b). A variety of the first is abundant as a 

 fossil in the later and softer limestones, often retaining very distinct bands of 

 brown color. The fossil variety (zonata V., now) is rather larger with a thicker 

 and firmer shell, larger umbilicus, and thicker callus than the living form. Both 

 varieties vary considerably in height of spire, size of umbilicus, and color. For 

 two series of comparative figures, see Part IV, Geology. 



