Vor. 2] Kofoid.—On Heterodinium. ay 
flagellar pore little more than 0.5 of the distance to the post- 
margin. 
Theeal plates of the normal type. Left intercalary confined 
to dorsal face. Suture lines heavy, deficient on right ventral 
area. Thecal wall covered with irregular polygons, mostly pen- 
tagonal, larger ones each with single central pore. Polygons 
relatively few, 41 on dorsal apical. In young individuals faint 
suture lines but no polygons are found. The ventral area is 
found as usual at the junction of the sutures on the ventral face 
of the epitheca. It is unusually large and contains the ante- 
riorly located reniform pit-like structure. 
Individuals thus far observed have been very hyaline and 
colorless or with pale greenish yellow chromatophores, reniform 
or irregular in shape. 
Dimensions:—leneth, 120-1254; transdiameter, 90-92p; 
dorso-ventral, 155; girdle width, 10»; polygons, 2-10p. 
Taken in vertical hauls from 90-100 fathoms to surface in 
June off San Diego. 
This species resembles H. h indmarcht (Murr. et Whitt.) im 
the type of reticulations, but differs from it in its more robust 
form, shorter epitheca and antapicals. 
Heterodinium trirostre (Murr. et Whitt.). 
Peridinium trirostre Murray and Whitting (’99), p. 327, Pl. 29, fig. 5. 
This species is shown to have the typical ventral plates of 
Heterodinium, the ventral pit and the deficient posterior list of 
the transverse furrow which is deflected posteriorly on the right 
antapical horn. 
The species is characterized by the presence of pointed an- 
tapical horns, the left showing a bifurcation into two apices. 
The epitheca is high, broadly cuneate with doubled lateral su- 
tures. The girdle is median, the transverse furrow being dis- 
placed only its own width. The reticulations are very coarse and 
heavy and exhibit more than the usual irregularity in form. 
Reported from 26° N. in the Atlantie. 
