1911] 



Kofoid: The Genus Gonyaidax. 



257 



to which the armature of fins and spines is developed on the sides 

 of this area is to a considerable extent a species character, as is 

 also the extent of the indentation which it makes in the terminal 

 antapical plate. 



The constituent plates of the theca are subject to diversifica- 

 tions in the various species only in the apical and anterior inter- 

 calary regions, those parts of the organism directed forward in 

 locomotion and therefore most subject to the impact of the en- 

 vironment. 



The total number of plates in the apical-intercalary region is 

 usually 3 (20 cases), occasionally 4 (6 cases), rarely 5 (2 cases), 

 or 6 (2 cases) or even 8 (1 case). The distribution of these plates 

 between the apical and intercalary regions varies. I arbitrarily 

 distinguish all those plates in contact with the apex as apicals, 

 and all others anterior to the precingulars as anterior inter- 

 calaries. The following table indicates the distribution of the 

 several types of plating among the species of the genus. 



Apical Plates in Species of Gonyaulax 



Number of Position 



Total Number of anterior of anterior 



Species plates Apicals interealaries intercalaries 



G. alaskensis, birostris, digitale, fra- 

 gilis, glyptorhynchus, inflata, ko- 

 foidi, pacifica, polygramma, scripp- 

 sae, spinifera, turbynei 3 3 



G. apiculata( ?), sphaeroidea 4 3 1 right ventral 



G. diegensis, hyalina(?) 4 4 



G. triacantha 5 3 2 dorsal 



G. joUiffei (^ Spiraulax joUiffei) 5 4 1 right ventral 



G. milneri 5 5 



G. polyedra 6 4 2 right ventral 



G. cerntocoroides 6 6 



G. catenata 8 4 4 dorsal 



G. highleii, mitra, palu.stris( ?), series ? ? ? 



An inspection of the table shows at once the predominance 

 of the 3'-0'^ combination and also that there is no marked 

 tendency for the deviations from this to conform to the lines 



