1911] Kofoid: The Genus Gonyaulax. 253 



The ventral pore is also found throughout the genus, but this 

 is present, though not hitherto described, in other genera, such 

 as Amphidoma, Goniodoma, Pyrophacus, and Centrodininm. It 

 therefore can not be regarded as a generic character. 



I. SPECIES CHARACTERS 

 1. The Extent op Differences between Species 



The specific characters which differentiate the thirty-six or 

 more species of this genus are of greatest variety and affect, in 

 one species or another, practically all the structural elements 

 which make up the organism (see Kofoid, 1906c). Not only is 

 this true for the genus as a whole, but it is also true to a large 

 degree for each species as a unit. It differs from its congeners 

 not merely in certain easily detected and quickly defined struc- 

 tural features which strike the eye at once, but in manifold 

 minor details which are less easily comprehended and can only 

 be described by a mass of minutiae and often accurately ex- 

 pressed only by statistics of proportional measurements. These 

 become evident as one works over the material, in spite of in- 

 creasing evidences of variation, which on the novice too often 

 leave the impression of inextricable confusion. Just as in the 

 case of the Gadidae, where Williamson (1910) has so clearly 

 demonstrated that the species are profoundly differentiated not 

 only in surface characters such as scalation and fin rays, but by 

 internal visceral and skeletal structures as well, so also in the 

 Dinoflagellata specific characters extend throughout the organ- 

 ism but are more easily comprehended in the less labile skeletal 

 structures. To this the work of Schmidt (1905, 1906) upon the 

 young stages of the various species of cod in the. North Atlantic 

 and North Sea has added equally striking evidence of the specific 

 distinctness of the eggs and fry, differences in dimensions, oil 

 drops, pigmentation, and the like, which the experienced eye 

 soon learns to utilize as an infallible guide to the separation of 

 these organisms in the early stages of their development. In a 

 like direction the work of the various divisions of the Interna- 

 tional Commission for the Investigation of the Sea has brought 

 to light the fact that sharply defined differences based on salini- 



