A PRELIMINARY WORKING KEY TO THE LIVING 

 SPECIES OF DERMATOLITHON 



By 



E. Yale Dawson 



Allan Hancock Foundation 



Before the outset of the Hancock expeditions, the vast Pacific Coast 

 of Mexico had never been visited by a student of the marine plants. To 

 be sure, collections had been obtained, more or less incidentally, by bot- 

 anists of other specialties, and a few reports existed in the literature; 

 but to a great extent the algae of the thousands of miles of shoreline, both 

 insular and continental, remained unexplored. The marine vegetation 

 of the off-shore waters was almost totally unknown. 



Dr. William Randolph Taylor was the first algologist to visit this 

 region, and through his eliforts on the Hancock Expeditions of 1934 and 

 1939 a splendid collection was made and subsequently reported upon 

 in 1945. 



In 1940 Captain Hancock directed the Velero III into the Gulf of 

 California, and, Dr. Taylor being otherwise engaged at the time, the 

 writer was privileged to begin his algological investigations in that fas- 

 cinating area. Subsequent expeditions under Hancock Foundation auspices 

 to various parts of the Mexican coast have resulted in the assembly at 

 the University of Southern California of the world's outstanding sea- 

 weed collection from that region. Publication on studies of this immense 

 collection, which now numbers several tens of thousands of specimens, 

 was begun by the writer in 1944 and has continued up to the present. The 

 most recent general contribution to the Pacific Mexican algal flora (Daw- 

 son 1954) dealt with the order Cryptonemiales, but did not include the 



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