324 University of California Publications in Zoology [Vol. 19 



At the posterior end of the sulcus and of the body arising from the 

 postmargin. is a short, stout, highly pigmented (dark orange), mobile, 

 permanent tentacle. Its location is posterior to the origin of the 

 longitudinal flagellum, where it is developed directly from the end of 

 the sulcus, a position comparable to that of the tentacle in Noctiluca. 

 Beyond this possession of a tentacle there are no other indications of 

 special relationship to Noctiluca. There is no marked vacuolation 

 and zoospores are \mknown. 



The third genus of the tribe Gymnodinioidae with a posterior 

 tentacle is Prot erythropsis now gen. Kofoid and Swezy MSS. with a 

 single species. P. crassicaudata Kofoid and Swezy MSS. This is a 

 highly specialized form (fig. G) with slightly more than one turn of 

 the girdle, which forms a descending left spiral with a displacement 

 of its distal end posteriorly for a distance of about (1.6 of the total 

 length of the body. The sulcus runs from near the apex to near the 

 antapex. Both transverse and longitudinal flagella are present in 

 their normal locations. There is an ocellus with melanosome and lens, 

 as in Pouchetia and Erythropsis. Arising from the margin of the 

 antapical section of the sulcus is a stout, ventrally recurved, pendant 

 tentacle, in length about 0.3 of the length of the body. This arises 

 immediately behind the base of the posterior flagellum. It is fore- 

 shadowed in the genus Pouchetia by species (P. maculata, fig. G) 

 which have a very mobile antapical region at one side of the sulcus. 

 The position of this tentacle with relation to the sulcus and posterior 

 flagellum is comparable to that of the tentacle of Noctiluca. Inter- 

 mediate stages leading towards P rot erythropsis are also seen in 

 Cochlodinium cavatum, in which the area adjacent to the sulcus is 

 protuberant and mobile. 



The genus Erythropsis is represented in literature by Hertwig's 

 (1884) original species E. agilis, and by two species described by Schiitt 

 as Pouchetia cornuta and P. cochlea, which have been transferreed 

 by Kofoid and Swezy (MSS) to Erythropsis. We have found the 

 tentacle on the former; the latter probably has it. Both have the 

 structure of Erythropsis. A fourth species has been described and 

 figured by Pavillard (1905) and Faure-Fremiet (1914) as E. agilis 

 Hertwig. yet it is not Hertwig's species but a new one, which is desig- 

 nated as E. pavillardi Kofoid and Swezy MSS. A fifth species, E. 

 < .rtrmh us Kofoid and Swezy MSS, appears in our text figure I. 



Faure-Fremiet (1914) has reversed the orientation of Erythropsis, 

 placing the tentacle anterior, and Dofiein (1916) has adopted this 



