252 University of California Publications in Zoology. [Vol.8 



the basis of the preparation of this paper affords an exceptional 

 opportunity not only for the appreciation and detection of minute 

 details of structural differences upon which the concept of species 

 is customarily built, but also for an ever growing realization 

 that other phases of the organism which may be designated 

 broadly as physiological or functional, rather than structural, are 

 just as profoundly and truly characteristic of species as are 

 those other concrete indications of activity of the living substance 

 which are recorded in more or less permanent expression in 

 form. It may be useful to sum up here both the morphological 

 and functional data and to give the impressions which this study 

 has made upon me with reference to the nature and relations of 

 both generic and specific characters. 



The generic characters of Gonyaulax are the displacement of 

 the girdle and the constant number of skeletal elements in the 

 hypotheca, girdle, and precingular series of plates, in all a con- 

 stancy in not less than twenty of the twenty-three to twenty-six 

 skeletal elements characteristic of the different species, and the 

 form and relations of apical 1'. If we divide the skeleton into 

 zones or belts of plates, as follows (a) apicals, three to five; (b) 

 anterior intercalary (incomplete), none to two; (3) precingulars, 

 six; (4) postcingulars, six; (5) posterior intercalary (incom- 

 plete), one; (6) antapical, one, we discover that the posterior 

 half of the skeleton, the girdle, and precingular belt are constant, 

 while the plates of apical region and adjacent intercalary region 

 are variable in number and position. The generic characters thus 

 inhere in the skeleton in and adjacent to the girdle and longi- 

 tudinal furrow (ventral area of this paper), structural features 

 moulded by the two fiagella. the prime ordinal characters of the 

 Dinofiagellata. They thus express, in so far at least as the main- 

 tenance of constant number is concerned, conservative ancestral 

 tendencies in the organism, and are directly related to the regions 

 of major activity. 



These characters are maintained with remarkable constancy 

 amidst a great diversity of external form, ranging from tlie 

 spherical as seen in G. sphaeroidea (pi. 16, figs. 41, 42), to the 

 greatly elongated seen in G. hirostris, or the polyhedral in G. 

 polycdra (pi. 17, fig. 43). 



