KOFOID AND SWEZY: UNARMOREU DINOFLAGELLATA 341 



The girdle starts far anterior, within 0.13 of the total length of the body from the anterior 

 end, ascends about 0.5 furrow's width in its proximal quarter, then descends in an ever steeper 

 spiral across the backhand down the ventral face to its junction with the sulcus at about 0.61 of 

 the total length of the body from the apex. The total displacement is one transdiameter at the 

 widest part of the body, or 0.5 the total length. The furrow is about 0.11 of a transdiameter in 

 width, nearly uniform to the distal end where it narrows slightly, and is not deeply impressed. 

 The transverse flagellum nearly encircles the body. The sulcus runs tlie whole length of the 

 body, passing anteriorly upon the epicone and almost completely encircling a central terminal 

 field as a slightly elevated button. It is very narrow and shallow in this region. It forms a 

 flat sigmoid curve on the ventral face and flares below the posterior flagellar pore located below 

 the junction of the distal end of the girdle, in a wide excavation 0.5 transdiameter in width 

 across the antapex. There is no flap over the sulcus and the right posterior margin is the longer, 

 a distinction generally attained by the left side in most asymmetrical dinoflagellates. The 

 posterior flagellum extends beyond the antapex for a distance of 0.7 the total length. 



The surface is finely and uniformly striate with equidistant longitudinal lines of equal 

 numbers on epicone and hypoeone. There are about 18 across the ventral face. The nucleus is 

 ellipsoidal, located slightly anterior to the middle with its major axis inclined a little to the 

 right. Its length is about 0.6 transdiameter. Numerous small greenish bodies of varying sizes 

 and subspheroidal shape of a high refractive index fill the cytoplasm. They appear to be reserve 

 food of a fatty nature. Near the posterior end is a small ellipsoidal body of yellow ochre color, 

 either a chromatophore or a small ingested food body. The general color is a suffused pale pea 

 green without localized chromatophores. 



Dimensions.— Total length, 40^6/* ; transdiameter at widest part, 22/^ ; dorso- 

 ventral diameter, IGi^- ; length of nucleus, 16iii. 



Occurrence. — T?are in the l:)eaeh sands off La Jolla, California, in July, 

 1914. 



Comparisons.^ — This species differs from all other species thus far described 

 in the genus (including all species in the old genus Spirodiniiim Schiitt) in 

 that it has the well defined loop of the sulcus around an apical button, as in 

 some forms of Cocldo(U)nam. The posteroventral excavation is also unusually 

 extensive. The fine striation on the surface is a common feature in many 

 species, though the uniformity on epicone and hj^ocone is not so generally 

 present. It is most like Gijrodinium herhnccum, sp. nov. and G. pingue (Schiitt) 

 (figs. DD. 6, 15) in general form, displacement of girdle, asymmetry and ten- 

 dency to truncate form of the antapex. It is, however, much smaller, A'yi'- instead 

 of 70ai in length, has the apical loop of the sulcus which Schiitt (1895) does not 

 figure, and has the girdle more anteriorly located as a whole. It also lacks the 

 rhalxlosomes or rodlets which appear to characterize Schiitt 's species. In its 

 doi'soventral flattening, green color, and small epicone it approaches the species 

 of Ampliidiniioii with which it is associated in the beach sands. It is the only 

 known arenaciphilous member of the genus Gyrodinium. 



