80 ANNALS NEW YORE ACADEMY OF SCIENCES 



genus is Hyria, which was seen by the writer only in the lower Amazon 

 and therefore probably does not belong to the older highland stock. I 

 did not see a dozen species of bivalves in Eio Guapore, which probably 

 indicates a -rather primitive stock, but they were very abundant in Eio 

 Uruguay, which indicates a great cenogenic evolution in this region. 



In a general way, the mollusca follow the same rules of distribution as 

 the fishes, but our knowledge, especially from accurate field data, of the 

 fresh-water bivalves of South America is entirely too meager to be used 

 in support of any theory. For example, Ortmann has found that some 

 of the bivalves have palpi, arrangement of gills and siphonal openings 

 like some of the African bivalves, but this may be due in both cases to 

 living in muddy, tropical water. Before such evidence can safely be used 

 to support any theory, much careful field work and experimental evi- 

 dence is needed. That is to say, we need dynamic and not static data. 



Many of the fossil bivalve shells in North America resemble living 

 forms in South America. Inasmuch as the soft parts are not preserved, 

 it will be very difficult to determine the paleotelic forms of bivalves which 

 were distributed. Von Ihering has listed 581 species of mollusca along 

 the coast of Brazil, 54 of which are known on both the Antillean and 

 African coasts, while 72 are found in common on the African and Bra- 

 zilian coasts. He does not appear to attach much importance to larval 

 distribution of these forms, but it is well known that some larval Crus- 

 tacea and mollusca are found on the high seas. Marine turtles also cross 

 the sea. Nichols has recently reported a case in which he thinks that the 

 mid-ocean whirlpool and side currents swept young Trachurus from the 

 coast of England to the coast of Florida. These ocean currents are well 

 known to the sailors, who often go far out of a direct route in order to 

 avoid them. In some places, when the winds are favorable, the one off 

 the Barbados Islands is said to run about five miles per hour. Currents, 

 therefore, may have transferred some mollusca between the South Amer- 

 ican and African coast along with sea weeds and other drift. Then, 

 again, a few forms could have been transferred by primitive sailing 

 vessels between the various ports. 



It is interesting to note in this connection that practically all of the 

 mollusca known from the Brazilian coast are reported from near larger 

 or smaller seaports. In other words, very little of the Brazilian coast has 

 been surveyed, and until regions remote from seaports are carefully 

 studied, too much stress must not be laid on the present list of mollusca. 

 Besides, the above lists of common forms on the African and Brazilian 

 coasts include such widely distributed (cosmopolitan) forms as Mytilus, 

 which could easily have gone south from the European and North Amer- 



