KOFOID AND MICHENER: DINOFLAGELLATES. 297 



that the dorsal spine at the fission plane is curved without bifurcation to 

 junction with the posterior one. Fin to dorsal side of posterior spine curved 

 anteriorly. Phaeosomes spheroidal. 



Length, antero-posterior, of body, 12 n, total, 53 n', dorso-ventral diameter 

 of midbody, 22 n, including fin, 25 n; phaeosomes, 1 n. 



Sta. 4720. 



HlSTIONEIS INCLINATA, Sp. IIOV. 



A minute species of simple structure slightly resembling H. crateriformis 

 Stein, but differing from his (1883), pi. 22, figs. 5 and 6, in shorter and less 

 antero-dorsal concavity on midbody, and in details of fin and collar structure. 

 Body subcircular, slightly concave antero-dorsally, epitheca considerably 

 elevated at base of anterior collar. Length and dorso-ventral diameter equal . 

 Antero-dorsal concavity less than 0.5 dorso-ventral diameter. Anterior 

 collar 0.35 dorso-ventral diameter in height, its apex very oblique with few 

 heavy longitudinal ribs. Posterior collar 0.5 dorso-ventral diameter in height 

 with dorsal and ventral sagittal ribs and simple convex transverse bars with 

 distal hyaline margin. Ventral and postero- ventral fins 0.35 dorso-ventral 

 diameter in height, terminating in broadly rounded lobe anterior to antapex. 

 Surface of midbody with fine regular mesh in central part of face, smooth 

 peripherally, about 12 prominent pores on right face. Phaeosomes spheroidal. 



Length, of midbody, 17 a«; total, 29 m,' dorso-ventral diameter of midbody, 

 13 m, total, 18 n. 



Sta. 4720. 



HlSTIONEIS INORNATA, Sp. nOV. 



A very minute, unadorned species resembling H. inclinata but with different 

 proportions of body and fins, unlike any previously described species. Body 

 rotund, flattened anteriorly, antero-dorsal concavity slight, nearly horizontal, 

 its length 0.55 of dorso-ventral diameter. Flagellar pore well forward on 

 antero-ventral curve. Length 0.8 dorso-ventral diameter. Inner collar on 

 slight eminence, its length 1.05 dorso-ventral diameters, neck very long and 

 slender, opening oblique, 0.5 dorso-ventral diameter. Posterior collar very 

 large, its opening 1.22 dorso-ventral diameters, inflated, with simple dorsal, 

 ventral and horizontal ribs and very low hyaline frill anterior to horizontal 

 bars. Ventral fin 1.5 dorso-ventral diameters in length and about 0.35 in 

 height, rounded and recurved posteriorly with stout ventral spine. Fission 

 ribs 0.33 dorso-ventral diameter in length. Fins and body absolutely smooth 

 and hyaline. A single row of pores at base of posterior collar, 10 on right face. 



Length, of midbody, 15 n, total, 33 n; dorso-ventral diameter, of midbody,, 

 16 ii, total, 18 fx. 



Sta. 4720. 



