Physical Geography of the Bahama Islands. 311 



Fisr. 4. The same. Jaw. 



Fig. 5. Helix lychnuchus. Mull. Jaw. 



Fig. 6. The same. Genitalia. The accessory gland of 

 the epididymis is not shown in the figure. It was broken oif. 



Fig. 7. The same. A group of central and lateral teeth 

 of the lingual membrane. 



Fiof. 8. The same. Marji-inal teeth from the left of the 

 median line of the lingual membrane. 



XXVIII. — On the Physical Geography of, and the Distribu- 

 tion of Terrestrial Mollusca in, the Bahama Islands. 



. By THOMAS BLA^"D. 

 Read April 28, 1873. 



The northern end of the extensive and remarkable group 

 called the Bahama, or Lucayos Islands, lies opposite southern 

 Florida, and from this point the islands stretch off in a 

 double series, nearly parallel to the trend of Cuba and San 

 Domingo, and terminate properly in the Turk's Island Bank, 

 on which are the last, and most easterly, of this chain of in- 

 habited islands, which extends about 600 miles, from within 

 70 miles of the coast of Florida, to within 100 miles of that 

 of San Domingo. 



The following brief description of the Banks and Islands, 

 defined generally by the 100-fathom line of soundings, is 

 taken principally from the valuable "Keport on the Bahamas," 

 by Governor Rawsou, which report accompanied the oflicial 

 "Blue Book" of that colony, for 1864; the soundings from 

 the charts issued by the U. S. Coast Survey, and the Hydro- 

 graphic Office of the U. S. Navy. 



The Little Bahama Bank. — This is the most northerly bank ; its north- 

 westeru point, Matanilla Reef, is 70 miles from the Florida shore, sepa- 



