KOFOID AND SWEZY: UNARMORED DINOPLAGELLATA 249 



This is a problematical organism and one which it is difficult to locate 

 systematically with the existins; data. It presents no G/juinodiiiinm charac- 

 teristics unless we consider it a nuitilated form. The extension on the girdle 

 over half the ventral face would point towards Heniidinium for its affinities, 

 rather than towards Gymnodiulimi. Until it has been redescribed, however, it 

 must be left among the species iiircrlac scdis. Its condition indicates ap])roach- 

 ing cytolvsis, and its structure suggests that its anteroposterior orientation has 

 been reversed. 



Gymnodinium rhomboides Schiitt 



Text figure Y, 15 



Gymnodimvm rhamboides Scliiitt (1895), p. 163, pi. 21, fig. 63. 



G. rhomboides, Lenimermann (1899), p. 358. 



G. rJiomboidcs, Paulsen (1907), p. 23; (1908), pp. 97, 99, fig. 136. After Schiitt (1895). 



G. rhomboides, Dotlein (1909), p. 461, fig. 412i_„ ; (1911), p. 527, fig. 472i_,. After Schutt 



(1895). 

 G. rhomboides, Lebour (1917fe), pp. 183, 190, 191, fig. 6. In part, includes G. fissum. 



Diagnosis. — A small species with symmetrical biconical body, its length 1.76 

 transdiameters ; girdle displaced twice its own width; sulcus extending from 

 near the apex to a short distance from the antapex; surface ridged. Length, 

 46i^. Atlantic or Mediterranean at Naples, Skagerak, and Plymouth Soimd, 

 England. 



Description. — The body is biconical or rhomboidal in shape, widest at the middle, its length 

 1.7 transdiameters. The epicene and hypocone are both symmetrically cone-shaped (about 60°) 

 with rounded apices. The hypocone exceeds the epicone in length by about 0.13 of its own length. 

 The epicone has a length on the left and right sides of the sulcus of 0.47 and 0.57 respectively 

 of the total length of the body. 



The girdle joins the sulcus proximally about 0.47 and distally 0.57 of tlie total length of the 

 body from the apex. It is slightly premedian in position as a whole. It has a width of about 

 0.09 transdiameter and is deeply impressed with overhanging borders. The sulcus invades the 

 epicone slightly more than midway between girdle and apex and extends posteriorl.y to a short 

 distance from the antapex as a slightly sinuous lin(>. The anterior flagellar pore is found at the 

 proximal junction of the girdle and sulcus and the posterior pore near the distal end of the 

 sulcus. 



The nucleus is a small spheroidal body, centrally located. Its diameter is about 0.4 trans- 

 diameter in length. The cytoplasm is filled with minute spherules of various sizes, most numerous 

 in the epicone and near the antapex. The surface is ribbed with faint longitudinal furrows ( ?), 

 about fifteen across the dorsal face, which are distinct near the girille and fade out near the 

 apices. 



Dimensions. — Length, 46m; transdiameter, 26i^; diameter of nucleus, 12/*. 



Occurrence. — This species was figured by Schiitt (1895) from the collec- 

 tions of the Plankton Ex])edition from the Bay of Naples oi- from the Atlantic. 

 It has been recorded from the Skagerak by Paidsen (1907) and from IMymouth 

 Sound, England, by Lebour (19\lb). 



