KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 135 



Reproduction. — Among the numerous iudividnals imder o])servation one 

 pair (text fig. U, 13) was found in what appeared to be a late phase of conju- 

 gation. Tliis conjecture is based upon the correctness of Stein's figures (1883, 

 pi. 17, figs. 25-27) of conjugation in Aniphidinmm lacustre. In his figures and 

 in our pair the two individuals are fused together in the regions of the ventral 

 pores and are slightly displaced anteroposteriorly. One pair could not be separ- 

 ated by manipulation and both in life and after fixation in Bouin's fluid and 

 staining in borax carmine was found to contain only a single spheroidal nucleus. 



In view of the lack of reliable information regarding fission, and especially 

 concerning the occurrence and manner of sexual reproduction in the Dinofiag- 

 ellata, it is quite possible, indeed highly probable, that this is only an early 

 stage in approaching binary fission in which the motor organs have divided but 

 the nucleus is still in the prophase. This sequence in the phenomenon of fission 

 is the usual one among some of the Eufiagellata (see Kofoid and Swezy, 1915) . 



Co:NrPARisoxs. — The grounds for including this species in the geniis Amphi- 

 dinium are at best but slight. The only morphological groimds are (1) the 

 left flap of the sulcus, (2) the dorsoventral compression, and (3) the relatively 

 small size of the epicone. These characters are found in whole or in pai't in 

 A. truncatum, A. scissum, A. asymmetricum, and A. dentatum (figs. U, 3, 1, 

 5,4). 



The relationships thus established appear to be more significant than the 

 form of girdle, which is the one character relating the species to Gymnodinium. 

 It is obvious, however, that the inclusion in Amphidinium of a species with so 

 large an epicone as that in A. corpulent um will necessitate an emendation to 

 the characteristics of the genus as defined by Schiitt (1896). 



Amphidinium corpulent um has a form of sulcus similar to that of A. scissum 

 encircling an apical lobe on the epicone, a left ventral flap along the sulcus as 

 in A. asymmetricum and dorsoventral compression as in A. scissum and A. 

 truncatum. It belongs, therefore, in that section of the genus. 



Amphidinium crassum Lohmann 



Text figure U, 18 



Amphidinium crassum Lohmann (1908), pp. 252, 261, 262, 366, 368, pi. 17, fig. 16; (1911), 



pp. 30, 31, fig. 126f. 

 A. crassum, Paulsen (1908), p. 96, fig. 130. 

 A. crassum, Ilerdman (1911&), p. 71; (1911c), p. 38. 

 A. crassum, Ostenfeld (1913), p. 338. 



A. crassum, Lebour (1917a.), table 1; (19176), p. 188, fig. 2. 

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



Diagnosis. — A minute species with ovoidal body, its length 1.50 trans- 

 diameters ; girdle anterior ; epicone minute. Length, 27/*. Baltic Sea off Kiel, 

 Germany, throughout the year. 



