Occasional Papers of the Museum of Zoology 11 



may form quite impassable thickets, while the large "nigger- 

 heads" of Melocactus and the spiked rosettes of Agave may 

 be about the only vegetation near the summits of the larger 

 monadnocks of older limestone. 



Nowhere can the vegetation truly be called a forest, 

 although, in protected places, especially on the leeward slopes 

 of the higher hills, larger trees, such as various species of 

 Bursera, Casearia honairensis, Bumelia ohovata, Capparis 

 jamaicensis, MacJiaonia Ottonis, and Guaiacuni officinale, do 

 form small, or even quite extensive, open groves. However, 

 the largest masses of natural foliage are furnished by the 

 poisonous "manzalienja" (Hippomane mancinella), which 

 forms quite dense and high tree-growths along the dry water- 

 courses of the inland region, especially on Curacao. Quite a 

 few of the shrubs and trees, such as Bursera semiriiba, shed 

 their leaves during the dry periods, while others, like Guaia- 

 cuni officinale, are evergreen. 



The native species of molluscs are quite largely confined to 

 the limestone outcrops, although certain of them extensi\ely 

 penetrate the more heavily wooded valleys of the higher hills, 

 especially of those in the Cretaceous rocks (fig. vii-19). At 

 the inner borders of the limestone rim (fig. vii-18), the soil 

 of the inland region is impregnated with the reddish deposit 

 that appears to be the principal residuum from the decomposi- 

 tion of coral rocks. Apparently enough calcareous material 

 remains in some of these places to support the limestone-loving 

 species.^' However, the extensive grass and brush covered 

 plains of the central region (fig. vii-17) are practically with- 

 out molluscan life. 



The limestone rim is broken by numerous "roois" and, more 

 rarely, by deep salt water channels that connect with the 

 broad, shallow lagoons behind the shore ramparts. Especially 

 on the island of Cura^-ao, the molluscs of each of these lime- 

 stone remnants form a quite isolated colony. The result of 

 this separation is most noticeable among the forms of the 



12 Included in the "calcareous soil" of Boldingh 's maps. For the 

 vegetation of the non-calcareous soils, see page 158, I. c. 



