194 Vniversity of California Puhlications in Zoology.^ [Vol. 8 



mistaken interpretation the basis of generic diagnosis as Stein 

 and his followers have done is to exclude from the genus species, 

 such as G. spkaeroidea, whose skeletal morphology would other- 

 wise compel their inclusion in the genus. It is therefore neces- 

 sary to eliminate this interpretation, and to confine the designa- 

 tion of longitudinal furrow (or the more widely applicable 

 term, "ventral area," which seems desirable on account of con- 

 ditions in Ceratium) to that part of the thecal wall in which the 

 fiagellum is found extending posteriorly between the two ends 

 of the girdle. This term ventral area was proposed by me (1909) 

 for this region in Peridi)iiiim and appears to be widely applic- 

 able in other genera. 



(5) The plates of the genus (Figs. A and B) are not as here- 

 tofore described, but. in all species which I have thus far 

 examined they are as follows: apicals, 8 to 6; anterior inter- 

 calaries, to 3 ; precingulars, 6 ; girdle, 6 ; postcingulars, 6 ; pos- 

 terior intercalary, 1 ; antapical, 1. The ventral area contains 

 one anterior plate indenting the epitheca, in the posterior margin 

 of which lies the flagellar pore, a group of about four small 

 intermediate plates and a large posterior plate. 



3. SKELETAL PLATES OF GONYAVLAX 



The apical plates (I'-C) are those in contact with the apex. 

 This does not have an open pore as sometimes indicated, but is 

 closed by a minute closing platelet {cl. pL, fig. A) which often 

 adheres to the top of apical 1' and covers the truncate apex. The 

 number of the apicals varies from three to six in different species. 

 At least three have been found in all species analyzed. It is 

 probable that jilate 1' has been overlooked in cases where two 

 apicals have been reported. Bifurcated and trifurcated apices 

 such as ]\Iurray and Whitting (1899, pi. 30, figs. 1-3) have 

 described in their inverted figures are due to the parting of the 

 apicals, a phenomenon very commonly observed in many species 

 of the genus, preparatory to ecdysis or the escape of the contents. 



In some cases as in G. apiculata and G. pohjedra one or more 

 of the plates in the apical region are crowded away from contact 

 with the apex. Such plates I have designated as anterior inter- 



