Vol. 3] Kofoid. — Dinoflagellata — New Species. 307 



This species differs from C". arcuatum in its subequal antapi- 

 cals, wider arc, and more contracted epitheca. 



Length, 350-425/x; transdiameter, 65-95/t; distance between 

 horns at level of base of apical, 290 to 370/^, ; between tips, 310 to 



400;a. 



Common in plankton of tropical character off San Diego. 

 Ceratium tenuissimum, sp. nov. 



PI. 29, figs. 32, 33. 



A minute species resembling C. carriense bnt much smaller 

 with delicate attenuate spreading antapicals. 



The midbody is very small, rotund, with erect apical, 3-8 

 transdiameters in length. The postmargin is scarcely differen- 

 tiated from bases of the antapicals and the postobliquity (15°) 

 is not very steep. The antapicals spread laterally with slight 

 major flexures, the right forming an angle of 50°-80° and the 

 left of about 90° with the apical. The antapicals are straight or 

 in many cases slightly reflexed 'posteriorly but less pronouncedly 

 than in a form of C. carriense which Schroder ( :06) has described 

 as C. hunclliauseni. All intergradations between straight and 

 curved horns are found. I do not regard such curvature as of 

 specific significance. It is more common in C. tenuissimum. than 

 in C. carriense as I have observed it. The antapicals are atten- 

 uate clistally and the tips are open or sometimes contracted. 

 Thecal wall hyaline, girdle often obsolete distally. The three 

 horns are usually subequal in length. 



This species is a fifth, or less, of the size of the typical forms 

 of C. carriense (=C. patentissimum Ost. et Schm.), which it 

 resembles in its proportions. I find no intergrading connections 

 and regard this smaller form as a distinct species. 



Length, 100-430/x; transdiameter, 35-45;u,; distance between 

 tips of antapicals, 215-850ju,. 



In oceanic plankton off San Diego. 



I retain Karsten's ( :06) name " recurvata" for the relatively 

 rare forms with the tips of the antapicals recurved posteriorly. 

 In the typical species the antapicals are not thus recurved. These 

 recurved forms do not belong, as Karsten indicates, to "Ceratium 

 tripos volans" but to the species here described. 



