The Mastigophora 145 



no marginal ridges (lists), whereas the Lissodiniidae and Podolampidae 

 have undergone apparently complete suppression of the girdle (197). 



The thecal plates are usually differentiated into several circular series 

 (Fig. 4. 21, K, L), and those in each series are conventionally numbered in 

 order, beginning at the left of the sulcal plane or the mid-ventral suture 

 (155). The apical plates (numbered V, 2', 3' . . .) extend to the apical 

 pore, or sometimes to a closing plate if the pore is closed. Anterior inter- 

 calary plates (la, 2a, . . .) lie between the apical and precingular plates. 

 Precingular plates (1", 2", . . .) extend from the apical or intercalary 

 plates to the girdle. The girdle plates (1, 2, 3 . . .) line the girdle. Post- 

 cingular plates {V", 2' ", . . .) lie in the hypotheca between the girdle 

 and the antapical plates (or posterior intercalary plates, if present). Pos- 

 terior intercalary plates (Ip, 2p, . . .) lie between the postcingular and 

 antapical plates. The a7itapical plates {\"",2"", . . .) cover the posterior 

 end. According to Kofoid's (155) system, the plate formula for Diplopsalis 

 lenticulata (Fig. 4. 21, G-J) would be written as 3'la6"5'"r'" (omitting 

 the girdle). 



Fainily 1. Glenodiniidae. These flagellates have a thin theca, with plates 

 which are not easily distinguished, and were at one time assigned to the 

 Gymnodinina. Most species are known from fresh water (74, 254). Gleno- 

 dinium (Ehrbg.) Stein (Fig. 4. 21, A-D) differs from Glenodiniopsis 

 VVoloszynska (Fig. 4. 22, M-O) in number of postcingular plates and in 

 a sulcus limited mostly or entirely to the hypocone. In Hemidinium Stein 

 (9, 11; Fig. 4. 21, E), the girdle extends only about a half turn. A palmella 

 stage (Fig. 4. 21, F), resembling that of Gleodinium, has been reported for 

 H. nasutum (11). 



Family 2. Gonyaulacidae. The thecal plates are distinct and one antapi- 

 cal plate is characteristic. Several species are known from fresh water (74, 

 254), but most are marine. Species of Gonyaiilax have attracted attention 

 as the source of mussel poisoning on the Pacific Coast (Chapter X) and 

 as a component of "red tide." 



The family includes Chalubinskia Woloszynska (Fig. 4. 22, E-H), Dinosphaera Kofoid 

 and Michener (157), Diplopsalis Bergh (178), Entzia Lebour (178), and Gonyaulax 

 Diesing em. Kofoid (156). Gonyaulax (Fig. 1. 5, A, B) has a plate formula of 

 l-6'0-3a6"66' "Ipl" ", while Dinosphaera (Fig. 4. 22, A-D) has 5 postcingulars and no 

 posterior intercalary. Diplopsalis (Fig. 4. 21, G-J) has the plate formula, 3'la6"5' "1" "; 

 Entzia, 4'l-2a7"5' "1" ", but otherwise similar to Diplopsalis. Chalubinskia (Fig. 4. 22, 

 E-H) has 3 postcingular and 1 antapical plates. 



Family 3. Peridiniidae. The thecal plates are distinct as in the Gonyaul- 

 acidae, but there are two antapical plates. Many species occur in fresh 

 water (74, 254); others are marine. 



The family includes Peridiniurn Ehrenberg (64; Fig. 4. 22, I-K), Amphidiniopsis 

 Woloszynska (Figs. 4. 17, C, 4. 22, L), Glenodiniopsis Woloszynska (Fig. 4. 22, M-O), 



