280 bulletin: museum of comparative zoology. 



lax in form and relations of apical V, in the plates of the hypotheca, in the 

 absence of an apical notch, and in the presence of a ventral pore. Type 

 species, P. sphaeroidea. 



Peridiniella sphaeroidea, sp. nov. 



A spheroidal species with shallow furrows, and plates with coarsely retic- 

 ulated patches. Body nearly spherical, its length 1.07 transdiameters, 

 girdle section circular, apex not elevated. Epitheca equals hypotheca. 

 Girdle descending, displaced 1.4 girdle widths, its ends not meeting mid- 

 ventrally by 1 girdle width, scarcely impressed, guarded by slightly everted 

 ridges. Ventral area scarcely indenting epitheca; extending about 0.6 

 distance to antapex, terminating in subcircular area occupied by posterior 

 plate of ventral area, nowhere deeply impressed. Plate formula, 4', 3 a , 7", 

 6, 6"' (?), l p , I"". Apical V, narrow, asymmetrical, bearing at its apex a 

 subcircular closing platelet, and joining the ventral area posteriorly as in 

 most species of Gonyaulax. Anterior intercalaries l a -3 a symmetrically 

 located on dorsal face as in Peridinium. Precingular 1" quadrangular. 

 Postcingular 1'" (?) less than 1 girdle width across and 2 in length. Posterior 

 intercalary large, asymmetrically located, as is also the antapical 1"". 

 Ventral pore midway between apex and proximal end of girdle at suture 

 between apical 2' and precingular 1", next to apical 1'. Surface with smooth 

 intercalary bands along meridional and tropical sutures, which isolate patches 

 of coarse irregular reticulations which show a tendency towards a quadrilateral 

 form. No lists or spines. 



Length, 52 n; transdiameter, 50 p. 



Sta. 4604. 



Peridinium annulatum, sp. nov. 



A large species with long, annulated apical and antapical horns. Belongs 

 in the group with P. fatulipes Kofoid (1907), pi. 5, fig. 30, (syn. P. tumidum 

 Okamura (?), P. tesselatum Karsten) and P. kofoidi Faure-Fremiet (1908), 

 pi. 16, fig. 12. It differs from P. fatulipes in greater elongation, narrower 

 hypotheca, wider postmargin of ventral area, less spreading antapical horns, 

 and in having the apical horn ringed with transverse riblets and the posterior 

 horn similarly adorned for a greater distance. It differs from P. kofoidi 

 in the long ventral notch which is not figured by Faure-Fremiet, in the apical 

 rings, in the much wider ventral area, and in the angle formed between the 

 antapical horns (22° in P. annulatum and 52° in P. kofoidi. Length 1.66 

 transdiameters; width of narrowest part of hypotheca 0.45 transdiameter 

 in girdle; length of antapical horns 0.5 transdiameter. Girdle not descending, 

 its distal end curved anteriorly, not impressed, with hyaline, ribbed lists. 

 Three dorsal anterior intercalary plates. Ventral area very wide, 0.22 trans- 

 diameter across, not deeply excavated and barely reaching postmargin. 



