1311] Kofoid: The Gchms Gonyaulax. 261 



characteristic. In G. polyedra we have a species which may occur 

 sporadically in overwhelming numbers, others, such as G. dic/italc. 

 poly gramma, spinifera, pacifica, catenata, diegensis and tria- 

 cantha may be locally common, or have a wide distribution, while 

 others, as in the case of most of the tropical species, have been 

 met with in small numbers and rarely, in a few cases only, singly 

 as yet. 



Fragility of the shell is another physiological feature of 

 Gonyaulax which is noticeable in the genus as a whole, but with 

 wide divergencies among the species. It is very rarely, for ex- 

 ample, that one finds an intact theca of G. fragilis, or its relatives 

 in the subgenus Steiniella. Likewise G. catenata is excessively 

 fragile, while G. polyedra and members of the hirostris group 

 are prone to part in the apical region. On the other hand in 

 most species the sutures on the right shoulder of the theca and of 

 the ventral area posterior to its anterior plate are separated with 

 great difficulty, if at all. 



The habit of ecdysis is allied to this proneness to disintegrate 

 on the part of the thecal wall. In G. polyedra, G. poly gramma, 

 G. spinifera and perhaps in others members of the group to which 

 these belong, the ecdysis is frequently seen, and it is no unusual 

 thing to find empty thecae of many of the species with dorsal 

 apical plates torn loose or missing, in the plankton. 



F. SUMMARY 



1. The genus is redefined on the basis of its skeletal mor- 

 phology. The skeleton consists of three (three to six) apicals, 

 no or one (none to four) anterior intercalaries, six precingulars, 

 six girdle plates, six postcingulars, the posterior intercalary, one 

 antapical and the plates of the ventral area. 



2. The so-called "longitudinal furrow" extending to the apex 

 is not in any morphological or functional meaning a furrow, but 

 merely the narrow apical plate 1', the homologue of the rhomb 

 plate of Feridinium. 



3. There is always a minute closing platelet in the apex and 

 a ventral pore (with several exceptions) on the right ventral 



