KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA \S3 



Synonymy. — This was originally figaired by Stein (1883) as Ampkidinium 

 operculntum Clap, and Lacli. and separated as A. opercidatiou var. stcini by 

 Lemmermanu (1910). 



Amphidinium sulcatum Kofoid 



Text figures IT, 10, 26 



Amphidinium sulcahnn Kofoid (IDOTff), pp. 299, 300, pi. 22, figs. 1-3. 



A. sulcatum, Lemmermanu (1910), p. 615. 



A. sulcatum, West (1916), p. .52, fig. 37. 



A. sulcatum, Herdmau (1911&), p. 72; (]911(:), p. 39. 



Diagnosis. — A rather large, laterally compressed species, its length 1.7 trans- 

 diameters ; girdle anterior ; sulcus extending from apex to antapex ; small yellow 

 ehromatophores. Length, 68m. Pacific off San Diego, June. 



Description. — The body is laterally compressed, broadly oval in lateral view, ellipsoidal in 

 ventral view. Its length is 1.7 trausdiameters, the dorsoveutral diameter 1.4 transdiameters at 

 the widest part. The greatest width of the body is midway between the girdle and antape.x. The 

 epicone is minute compared with the hypocone, its length being 0.14 of the total length of the 

 body. It is highest laterally and dorsally and hollowed out towards the sulcus, which passes 

 dorsally beyond the apex. The hypocone is broadly rounded posteriorly, and very deeply 

 channeled ventrally by the sulcus, which deepens as it passes posteriorly from the flagellar pore. 



The girdle is anterior in position, sliglitly enlarged on the left side and narrowed at its distal 

 end, which is displaced posterioi'ly by about the width of the proximal end of the furrow. The 

 furrow is very deeply imbedded and its proximal width is more than twice that of the distal 

 region. The sulcus extends from the dorsal half of the epicone to the antapex. It is a narrow 

 channel anteriorly with a depth at the flagellar pore of 0.25 of the dorsoveutral diameter at that 

 level and deepens posteriorly until at the antapex it reaches nearly 0.5 of the dorsoventral 

 diameter. The right lip of the furrow is somewhat higher than the left. 



The surface is covered with a thin hyaline membrane. The nucleus is a spheroidal body in 

 the middle of the hypocone. It is filled with moniliform chromatin strands and two polar 

 centrosomes (?) or nucleoli sunk in its substance. A pyriform vacuole lies near the flagellar 

 pore, but its connection with the opening is not evident. A large amyloid bod.y is present near 

 the nucleus and surrounding it are small angular yellowish ehromatophores. The cytoplasm is 

 dense and coarsely granular. 



Dimensions. — Length, 68;^; transdiameter, 35/'; dorsoventral diameter, 55/^; 

 diameter of nucleus, 15/^. 



Occurrence. — Taken in a vertical haid of 165 meters to the surface, 10.5 

 miles off San Diego, California, June 14, 1904. 



Comparisons. — This species stands alone among the species of Ampliidinium 

 in having a laterally compressed l)ody. It is, however, tentatively placed with 

 the dorsoventrally compressed forms in the subgenus Amphidiniurii. Possiljly 

 a separate subgenus should be established for the species. The truncate anterior 

 end recalls the condition in A. herdmani and A. truncatum. 



