184 University of California Publications in Zoology. [Vol. 6 



nearly the same position, proportions, and relationships as in 

 that genus. The five spines, one ventral, three antapical, and one 

 dorsal, all lie nearly in the sagittal plane as does the posterior 

 fin in the Dinophysidae. The two ventral fins upon each side of 

 the ventral area are likewise arranged in a general way as are the 

 lins (if Phalacroma. But the skeletal morphology is in all cases 

 analyzed strictly of the Ceratocorys type and never of the 

 Dinophysis type. The sheathed spines bear typical distal brushes 

 and are sometimes connected by membranes. The spine of the 

 ventral fin is of the Ceratocorys type, bearing no resemblance in 

 structural details to those of the ventral fins of the Dinophysidae. 

 The surface is evenly pitted with small pores. The sutures, in 

 or near the sagittal line, as I have found them, are not sinuous 

 as in the Dinophysidae and as figured by Entz (1902). The 

 sutures are not marked by fins except in the sagittal region or 

 by thickenings as in the armatum group, and are not readily 

 distinguished. They can, however, be found with the oil immer- 

 sion and the plates can be isolated by pressure and treatment 

 with reagents. The whole superficial make-up of this C< ratocorys 

 is must strikingly similar to that of the Dinophysidae, for 

 example in the matter of spines to Dinophysis uracantha, and 

 in form of body, ventral fins and girdle to Phalacroma poro- 

 dictyum. Resemblance so striking as this occurring among the 

 ll\ tnenoptera or Lepidoptera might easily be regarded as a case 

 of "mimicry." There is, however, among these organisms no 

 satisfactory evidence to justify such an interpretation, for we 

 have as yet no evidence of selective feeding on the part of larvae 

 and other organisms of the plankton which prey upon tin' Dino- 

 flagellates. The smaller plankton organisms are either taken 

 in masse, as in Salpa, or apparently without discrimination, as 

 by the Copepoda. The species in question are also, in so far at 

 leasl as observation has gone, altogether too rare to justify reason- 

 ably an interpretation of this resemblance as mimicry resulting 

 from natural selection. Gonyaulax ceratocoroides resembles in a 

 very striking way Ceratocorys horrida whose numbers are suffi- 

 cient to supply the basis for its use as a model. But in this case, 

 as well as in that of C. jourdani, it seems more probable that the 

 resemblances rest upon convergence in structure to meet common 



