VoL. 2] Kofoid.—On Heterodinium. 359 
Heterodinium hindmarchi (Murr. et. Whitt.). 
Peridinium Hindmarchii Murray and Whitting (799), p. 326, Pl. 29, 
figs. la, b. 
This is plainly a Heterodinium as it has the characteristic 
ventral pit in the central expansion of the median ventral suture 
of the epitheea, a short longitudinal furrow and the deficient 
distal posterior list of the transverse furrow. The plates are 
not shown but the presence of the left intercalary plate is sug- 
gested in the figure. 
The species is characterized by the long stout widely sepa- 
rated antapicals, elongated epitheea, and coarse reticulations. 
Reported from tropical Atlantic from Panama to 34° N. 
Heterodinium scrippsi sp. nov. 
Pl. 17, figs. 1-5. 
A large species with short antapicals, scoop-shaped epitheeca 
and coarse irregular reticulations. The body is subheptangular 
in face view, swollen at the girdle, and with shallow posterior 
bifureation. The length is 1.5 and the dorso-ventral diameter 
0.7 times the transdiameter. The epitheca is long, and its alti- 
tude is about 0.8 transdiameters. The ventral face is flattened 
and hollowed out anteriorly and thins out laterally to the doubled 
suture lines on the angular margin between the apical plates. 
Posteriorly the epitheca flares out to meet the girdle. The lateral 
margins have rounded shoulders about two-thirds of the distance 
from the girdle to the apical pore which rises from the anterior 
end in a fully developed apical horn. <A short ventral slot-like 
extension of the apical pore such as is found in Peridinium, fol- 
lows the midventral suture for a short distance. 
The hypotheca is shorter than the epitheea and in the mid- 
ventral line has scarcely 0.6 its altitude. To the tip of the long 
left antapical is 0.75 transdiameters. It is somewhat angular, 
is flattened ventrally and excavated in the midventral region 
between the antapicals. The dorsal side has considerably more 
flare toward the girdle. The antapicals are short and divergent, 
the right being more oblique than the left. The tips are acute. 
