KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 337 



Gyrodinium truncatum sp. nov. 



Plate 1, figure 3; text figure CC, 5 



DiAGXosis. — A small species with sulwvoidal body, its length 1.62 transdi- 

 ameters; girdle submediau, a desceuding left spiral, displaced 0.4 transdiain- 

 eter ; sulcus short on epicene, extending to antapex on hypocone ; color, yellow 

 green shading to yellow ochre posteriorly. Length, 57/*. Pacific off La Jolla, 

 California, July. 



Description. — The body is broadl.v ovoidal or almost bieonical, tapering at both ends with 

 truncate apex, widest posterior to the middle, its length 1.62 transdiameters at the widest part, 

 which is near the girdle. In cross-section the body is nearly circular. The epicone has a slightly 

 greater length than the hypocone, but its actual size is about the same. It is truncate conical 

 of about 60° in shape, contracted towards the apex, and has a length on the left and right sides 

 respectively of about 0.38 and 0.63 of the total length of the body. The hypocone is rotund 

 anteriorly, tapering abruptly posteriorly to an acute tip, with the left side more convex than the 

 right. It has a length on the left and right sides of about 0.57 and 0.33 of the total length of 

 the body. 



The girdle is submedian in position, its proximal end joining the sulcus at a distance from 

 the apex of 0.38 and its distal end 0.63 of the total length of the body. Its course around the 

 body is that of a descending left spiral, displaced posteriorly 0.4 transdiameter. The furrow 

 has a width of about 0.07 transdiameter and is deeply impressed, with a rounded outline, which 

 undercuts both borders slightly. The sulcus invades the epicone for a short distance as a rather 

 shallow trough and extends posteriorly in a slightly sinuous line which fades out near the 

 antapex. The anterior flagellar pore is located at the proximal junction of the girdle and sulcus, 

 the posterior pore midway of the distance between the distal junction and the antapex. 



The nucleus is a renifonu body filled with moniliform chromatin strands and is found in the 

 posterior part of the body, in the region of the posterior pore, with its long axis in a transverse 

 plane. Its major and minor axes are 0.71 and 0.31 transdiameters in length respectively. 



A small saeklike pusule opens into each flagellar pore. The cytoplasm is very finely granular, 

 clear and transparent with a few oil drops scattered througli it, and contains a number of food 

 bodies, evidence of holozoic nutrition. In the anterior portion of the body was a large food mass 

 vellow grey in color. Near it was a smaller, greenish refractive body and in the antapical 

 region another one, yellow ochre in color. The general color of the organism is greenish yellow, 

 shading to yellow ochre posteriorly. A thin-walled, hyaline cyst, somewhat larger than the body, 

 invested the organism. 



DiiiENSiONS. — Length, 57m ; transdiameter, 35m ; axes of nucleus, 21m and 11m ; 

 length of cyst, 67m. 



OccuERENCE. — A single individual was taken July 11, 1917, with a No. 25 

 net, in a haul 4 miles ofE La Jolla, California, from 80 meters to the surfai^e 

 and in a surface temperature of 19-8 C. 



Comparisons. — This is one of the species of Gyrodinium, which shows the 

 nearest approximation to the Gymnndinium tj-pe of the girdle arrangement, 

 and is probably one of the connecting links with tliat genus. It is one of the 

 more generalized species in Gyrodiuium, and in that respect resembles G. ovum, 

 (Schiitt) and G. foUaceum nom. sp. nov. (figs. CC, 8, 18), lacking, however, the 

 chromatophores of the latter species. 



