286 bulletin: museum of comparative zoology. 



end slanted posteriorly on ventral face. Anterior ridge salient, shelf-like; 

 posterior wholly deficient throughout, its position suggested by a line of pores. 

 Ventral area occluded between girdle ends, sigmoid, fan-shaped toward post- 

 margin where it bears two symmetrically placed, ventro-posteriorly pro- 

 jecting acicular spines, a girdle width in length. Another spine and fin guard 

 the left margin of the area. Surface wholly smooth, except for faint reticu- 

 lations in girdle. Distribution of pores, which are separated by groups of 

 pore-free intercalary bands, suggests the plate arrangement. Anterior 

 intercalary l a on left shoulder marked by but a single pore. 



Length, 40 /jl; transdiameter, in girdle, 35 n, on anterior ridge, 40 n. 



Sta. 4697. 



Heterodinium spiniferum, sp. nov. 



With the general form of Peridinium fatulipes Kofoid. Length 1.6 trans- 

 diameters in girdle. Epitheca subconical, with tapering apical horn and 

 angled right shoulder, exceeding hypotheca which has two spreading, atten- 

 uate, subulate antapical horns, 0.42 transdiameter in girdle in length. Girdle 

 slightly descending, displaced only 0.25 girdle width, its anterior ridge pro- 

 jecting, shelf-like, the posterior almost wholly deficient. Ventral area spread- 

 ing, fan-shaped. Ventral pore nearly midway between truncate apex and 

 girdle, at anterior end of elongated, pointed, smooth median area. Surface 

 coarsely and irregularly reticulate, postmargin denticulate. 



Length, 80 n; transdiameter, in girdle, 50 m, on anterior list, 60 m- 



Sta. 4695. 



Centrodinium expansum, sp. nov. 



A large species resembling C. elongatum but differing in its greatly expanded 

 girdle, and relatively shorter and less twisted antapical horn. Body elongated, 

 laterally compressed, with blunt apex and elongated asymmetrical antapex. 

 Length 2.85 transdiameters. Girdle section elliptical, major axis dorso- 

 ventral 1.12 transdiameters in length. Epitheca, in dorsal view, less than 

 hypotheca, tapering, conical, deflected to the left, with apex unevenly trun- 

 cated and inclined to the left, widely flaring at the girdle, its altitude 1.2 

 transdiameters. In lateral view the epitheca resembles that of C. elongatum, 

 but is a little higher, fuller along dorsal margin, and with a more rounded apex. 

 Hypotheca in lateral view similar to that of C. elongatum but with shorter 

 horn. Its total length 1.3, length of horn 0.7 transdiameters. Horn twisted 

 90°, curved to dorsal side with a claw-like tip concave on the right face. 

 Girdle premedian, descending, displaced one girdle width, deeply impressed, 

 with stout salient ridges. Fins upon either side of the elongated ventral area. 

 Surface smooth, sparingly porulate. 



Length, 107 n; transdiameter, 41 /*; dorso-ventral diameter, 46 p. 



Sta. 4711. 



