1911] Kofoid: The Genus Gonyaulax. 259 



ments of the two flagella bring a current of water sweeping over 

 the surfaces of these plates. In other words they constitute a 

 region of maximum contact with the environment. The direct 

 action of the environment as a potent modifying agent in the 

 process of speciation is thus strongly suggested. 



The surface of the thecal wall of Go)iyaulax exhibits nearly 

 all of the modifications found in the whole order of Dinoflagel- 

 lata ranging from the smooth almost undifferentiated spineless 

 and finless G. scrippsae to the exceedingly rugose G. milneri and 

 the long-spined G. ceratocoroides. Minute quadrangular areo- 

 lations are seen in G. triacantha (pi. 11, fig. 13), pits which pass 

 over into a coarse mesh work in G. poUjedra (pi. 14, fig. 31), 

 linear striae in the poUjgramyna (pi. 17, fig. 47) group, and ver- 

 miculate in certain species of the subgenus Steiniella (pi. 17, fig. 

 46), while in many instances a reticular mesh work, usually quite 

 characteristic of the species is found. These surface markings 

 are peripheral characters in immediate contact with the environ- 

 ing medium and more than any other feature of skeletal organ- 

 ization exhibit variation in respect to age of the theca, but espe- 

 cially with reference to temperature, salinity and perhaps to 

 more subtile chemical modifications in the water in which they 

 are found. The proof of this statement lies in the fact that most 

 of the individuals taken at one time in a given locality will bear 

 a characteristic facies, expressed in Gonyaulax in surface mark- 

 ings, and this may differ in greater or less degree from the same 

 species taken elsewhere, or at the same locality at another season. 



The marked asymmetry expressed in the inequality of the 

 two posterior horns in Peridinnmi and Ceratium is hinted at in 

 the tendency toward antapical asymmetry seen in the larger mem- 

 bers of the polygramma series, as for example in G. pacifica. It 

 is perhaps to be correlated in all instances with the proximity of 

 this region to the posteriorly extending flagellum with the current 

 of water it produces sweeping backward in the immediate neigh- 

 borhood of the left antapical region. 



Physiological Characters 

 In the matter of size each species has its characteristic limita- 

 tions, the range in size increasing with the amount and geographi- 



