306 University of California Puhlications. [Zoology 



The center of the spiral lies just anterior to the base of the apical 

 horn and its plane is oblique from the left dorsally to the right 

 ventrally at an angle of about 30°-45° to the frontal plane. The 

 diameter of the coil is 1-2 transdiameters. The spiral is quite 

 regular, the interval between the turns being 2-3 times the diam- 

 eter of the horn and increasing slightly from the center to the 

 periphery of the coil. The surface reticulations of the midbody, 

 postmarginal fin, form of the right horn and dimensions are sim- 

 ilar to those of C. rcticulatmn in its longer horned forms. 

 In oceanic plankton of tropical character off San Diego. 



Ceratium schranki, sp. no v. 



PI. 28, figs. 29a-31. 



Ceratium {tripos var.) arcuatum (in part), Okamura and Mshi- 



kawa (:04), p. 122, pi. 6, figs. 3, 3a. 

 Ceratium tripos arcuatum (in part), Entz (:05), pp. 107, 109, Taf. 



5^ Figs. 31, 32, Taf. 6, Fig. 45. 

 Ceratium tripos lunula (in part), Karsten ('06), pp. 142-143, Taf. 



20, Figs. 12o, 12&. 



A large robust species related to C. arcuatum, having regu- 

 larly curved, balanced, often subequal antapicals, and almost 

 semicircular posterior outline. 



The midbody is less rotund than in many species of the tripos 

 group and the margins of the epitheca are but slightly convex or 

 even concave. The apical horn is not so much displaced as in 

 C. arcuatum and is stout and heavy and often relatively short. 

 The distal part of the girdle is crowded close to the base of the 

 right horn. The postmargin of the midbody is not set off from 

 the bases of the antapicals by any indentation and its curvature 

 is continued without marked change in its radius till the antapi- 

 cals attain a direction parallel to the apical where the curvature 

 slackens and the horns continue distally with little, if any, curva- 

 ture toward the axis. The posterior border is thus a semicircle 

 whose radius equals approximately two transdiameters. The 

 distance between the antapicals at the level of the base of the 

 apical is 3-3.5 transdiameters. The antapicals are stout and 

 heavy with closed pointed tips and are often approximately equal 

 in length. Occasionally the right horn exceeds the left in length. 

 Often found in chain formation. 



