If*!!] Kofoid: The Genus Gonyaulax. 197 



antapex. Thecal wall (text figs. A-D) consisting of one to six 

 apical plates {l'-6'). none to three anterior intercalaries 

 (I'^-S"), six precingulars {l''-6"), six girdle plates (1-6), six 

 postcingulars, {l'"-6"'), one posterior intercalary {1'^), and one 

 (i"") antapical. The longitudinal furrow occupies the whole of 

 the ventral area (v. a.) which slightly indents the epitheca and 

 consists of one anterior, about four intermediate and one posterior 

 plate. The midventral plate {!') of the apical series is usually a 

 narrow plate extending posteriorly to a junction with the anterior 

 plate of the ventral area, thus parting precingulars i" and 6"'. 

 When guarded by lateral ridges it simulates an anterior extension 

 of the longitudinal furrow. It bears at its apex a delicate 

 extension, the closing platelet which covers the apical region. 



Surface smooth or rugose with major thickenings along suture 

 lines and minor ones on plates forming a regular or irregular 

 polygonal mesh of varying size, often with vermiculate, longitu- 

 dinal elements predominating, sometimes spinulate. Furrows 

 with or without lists which in many species are ribbed or spin- 

 ulate. One or more antapical spines sometimes present, rarely 

 with sheathed spines of the Ceratocorijs type. Plates porulate, 

 with pores in centers, angles or nodes of the mesh. A peculiar 

 large ventral pore {v. po.) occurs to the right of the midventral 

 line usually near the suture between apical 1' and the plate to 

 its right. Theca divided obliquely in fission. Ecdysis frequently 

 seen. Chromatophores yellow to dark brown, often dense. In 

 fresh, brackish and marine waters from boreal to tropical 

 regions. 



III. Comparisons With Other Genera 



The presence in Gonyaulax of a single large antapical plate 

 separates this genus at once from Pijropliacus and Podolanipas (4 

 antapicals), GoHiodonia, Frotocc ratiion, and BlepJtarocysta (3 

 antapicals), and from Diplopsalis and Peridinium (2 antapicals). 

 The hypotheca of Gonyaulax is identical with that of Steiniella 

 and Ceratocorys [see Kofoid 1910] in its skeletal elements. 

 The epitheca of the latter genus is distinguished by having five 

 instead of six precingulars as in Gonyaulax. 



