360 ORTMANN — DISTRIBUTION OF DECAPODS [Aprils, 



Antilles from the mainland, there was left on these islands an iso- 

 lated stock of primitive freshwater crabs, now known under the 

 name oi Epilobocera. On the mainland, these primitive forms dis- 

 appeared, or changed into what is now known as the genus Potamo- 

 carcinus, and although in the beginning of the Tertiary the conti- 

 nental range of this genus was much cut up, chiefly in the region of 

 the isthmus, the different parts were reunited in the Miocene, form- 

 ing a unit that extended from northern Central America to Trinidad 

 and Guiana. This explains the uniform distribution of Potamocar- 

 cinus over this region. In the later Tertiary we had a second union 

 of the Greater Antilles with northern Central America, which 

 explains the immigration of identical species of Potamo car cinus 

 from Mexico into Cuba and Hayti. The Lesser Antilles were 

 probably connected in the later Tertiary with Venezuela, and a 

 species of freshwater crabs reached them by this way. 



c. Relation of Venezuela to the rest of South America. The 

 Orinoco Valley. 



The northern coast range of Venezuela belongs, as has been 

 stated, to Central America. To the south, on the slope toward the 

 Orinoco, it is fringed by extensively developed Cretaceous deposits, 

 which are also known from Trinidad in a similar position. These 

 deposits are said to belong to the Lower Cretaceous (Suess, 1885, 

 p. 688), and to extend vvestward far into Colombia. To the south 

 of this zone, in Venezuela, there are (Suess, ibid.^ younger Tertiary 

 marine beds, which, in part, enter this region through a depression 

 extending southward from the Bay of Barcelona on the northern 

 coast of Venezuela. 



This would indicate that during the Lower Cretaceous, the old 

 Antillean continent was bounded on the south by sea (see above, p. 

 343), which separated it from the old granitic masses of Guiana. 

 The apparent lack of Upper Cretaceous deposits, with the excep- 

 tion of a small region of western Venezuela, points to the assumption 

 that at the end of the Mesozoic time (Upper Cretaceous) both 

 regions were connected. Then again, in the later Tertiary, they 

 were separated, at least in part, by sea that entered into the 

 Orinoco valley (Suess, 1888, p. 161). 



The Lower Cretaceous sea not only separated Venezuela and 

 Guiana, but apparently continued westward, into Colombia, 

 Ecuador and Peru. Indeed, there are in the western chain of the 



