1911] Kofoid: The Genus Gonijaulax. 239 



calaries those between these plates and the precingulars; and also in the 

 fact that two additional plates are here defined for the apical region for 

 the first time. A minute but perfectly distinct plate, 4p, lies between the 

 two intercalaries, ]", 2", and the apex. This plate appears in the figures 

 of Biitschli (1885b) and Torrey (1902) but is not treated as a separate 

 plate by them. When the structure of the apical region of G. polyedra 

 is considered in the light of that of other species of the genus, the hom- 

 ologies of the parts are clearly as follows: the so-called anterior extension 

 of the longitudinal furrow is a ventral apical 1', homologous with the 

 diamond-shaped plate of Peridinium. The intercalary region of the right 

 shoulder contains two plates instead of one as in Spiraulax jolliffei. 

 Gonyaulax aphaeroidea and G. apiculata, the adjacent apical region is 

 greatly reduced in size and the territory which is occupied by apical 3' 

 in such species as G. poly gramma, a typical Gonyaulax with three apicals, 

 is subdivided into two plates, one of which, 3', on the right dorsal shoulder 

 is of.some size while the other, 4', is the minute plate in question. It is 

 quite probable that the extra intercalary, 1", adjacent to apical 4' has 

 been split off from its lower edge and also belongs in the territory of 

 apical 3' of several species of the polygramma and spinifera groups, 

 where its presence is suggested by the surface markings indicative of an 

 incipient suture. The position and relations of the two large plates on 

 the right shoulder are those of the intercalaries and the small plate is 

 plainly one of the apical series. The disposition of the plates here pro- 

 posed enables us to homologize the plates of the apical region of polyedra 

 with those of other species of the genus. 



There is some variation in size of apical 4' (compare plate 14, figure 

 28, and plate 12, figure 20), which gives rise to certain modifications of 

 the relations of the plates to the elliptical apical area which contains 

 the closing platelet (el. pi, pi. 12, fig. 20). Ordinarily the plate desig- 

 nated as anterior intercalary f« does not come into contact with this 

 apical region (pi. 12, figs. 18 and 20). In one case (pi. 14, fig. 29) of a 

 reduced apical 4' this intercalary impinges upon the apical region. 



In another instance a third right dorsal anterior intercalary plate 

 (x, pi. 14, fig. 28) appears as an extra plate which seems to have devel- 

 oped at the expense of the equatorial ends of apical 3' and intercalary 

 1". This is the only instance thus far detected in any species of the 

 genus Gonyaulax of a variation in the number of plates. The genus 

 exhibits a noteworthy rigidity in this respect. 



Apical 1' is much wider than figured by Stein (1883) and is somewhat 

 irregular in outline, widening at the apical-intercalary suture (pi. 12, 

 fig. 20). An apical notch has not been found but the ventral pore {v. po.) 

 in the right margin of apical J.' opposite the middle of intercalary 

 ;?" was noted. At its apical end plate 1' appears to include the region 

 designated in other species as the closing platelet {cl. pi., pi. 12, fig. 20). 

 It contains a minute hyaline oblong area. Apical 2' is large, covering the 

 left apex. Precingulars 1" and 6" are parted by the ventral area and 

 apical 1' which are joined in the midventral line. Precingular 6" is pen- 

 tagonal. Posteingular 1"' is a very slender plate at the edge of the ventral 

 area and has been overlooked in all previous accounts of the species. The 



