KOPOID AND SWEZY: UNARMORED DINOFLAGELLATA 285 



Gyrodinium acutum (Sclilitt) 



Text figure CC, 7 



Gymnodinium spiralc var. acuta Schiitt (1895), pi. 21, fig. 66. 

 Spirodiiiium spiralc var. acutum, Ijemmermann (1899), p. 359. 

 S. spirale var. acuta. Schroder (1900), p. 13. 

 S. spirale var. acuta, Pavillard (1905), p. 47. 



Not Spirodinium spirale var. acutum, Lebour (1917&) (= Gyrodinium hritannia nom. sp. 

 nov. ) . 



Diagnosis. — A large species with slender, fusiform body, its length 3.32 

 transdiameters ; girdle a descending left spiral Avith slight overhang and dis- 

 placement of 0.93 transdiameter ; sulcus extending from apex to within a short 

 distance of the antapex. Atlantic ( "?) or Bay of Naples. 



Description. — The body is slender fusiform, wider posteriorly, tapering to both apices, its 

 length 3.32 transdiameters at the widest part, which is in the posterior third of the body. The 

 hypocone exceeds the epicone in size, its length being greater by 0.12 of its own length and its 

 transdiameter by 0.09. The epicone is elongate conical, about 32°, with a narrow, blunt apex. 

 It has a length on the left and right sides of 0.32 and 0.60 respectively of the length of the body. 

 The antapex is slightly wider than the apex and blunt. 



The proximal end of the girdle joins the sulcus at a point distant from the apex 0.32 of the 

 total length of the body. Its course around the body is that of a rather steeply descending left 

 spiral, with tlie distal end joining the sulcus at a distance from the apex of 0.60 of the total 

 length of the body. The furrow has a width of about 0.06 transdiameter and is deeply impres.sed 

 with smootli borders. The sulcus begins at the apex and extends posteriorly in a slightly sinuous 

 line to within a short distance of the antapex. The anterior flagellar pore is found at the junction 

 of tlie girdle and sulcus, the posterior pore midway between the distal junction and the antapex. 



The nucleus is an ellijisoidal body lying near the midregion of the cytoplasm. It is filled 

 with coarse, moniliform chromatin strands which lie in the plane of its long axis, which is slightly 

 oblique to the longitudinal axis of the body. Its major and minor axes are 0.76 and 0.41 trans- 

 diameters in length respectively. 



A small sacklike or club-shaped pusule opens into the anterior flagellar pore. The cytoplasm 

 is finely granular. A double-contoured periplast is shown in Schiitt's figure (text fig. CC, 7), 

 but no reference is made to it in text or description. A periplieral layer of "Randstiibschen" 

 or slender rodlets occupies a large proportion of tlie interior of the bod.y. These are arranged 

 nearly perpendicular to the surface, and probably correspond to the small blue-green rodlets 

 found in many of our own specimens, as in G. ohfusuiti (text fig. DD, 3). In the anterior part 

 of the body is a large, closely massed cluster of small sjiherules. No notes have been given by 

 Schiitt on the color of the organism. The surface is witliouf striae. 



Dimensions. — Length, 143/*; transdiameter, 43m; axes of nucleus, 33^ and 19/*. 



Occurrence. — Figured liy Schiitt (1895) from material secured hy the 

 Plankton Expedition, presumably from the Atlantic or from the Bay of Naples. 



SYNOXY:krY. — This was originally figured by Schiitt (1895) as Gymnodinium 

 spirale var. acxdn and later transferred by Leinmermann (1899) to the genus 

 Spirodinium as S. spirale var. acutum. 



CojiirARisoNS. — This species is nmch larger than Gyrodinium spiralc. l)eing 

 143f- in length as compared with 60/* to 100/* of the other species. It also differs 



