96 MEMOIKS OF THE UNIVERSITY OF CALIFOKNIA 



A. scissmn, A. truncation. A. doitntniii. with one representative eacli of the 

 genera Gijnniodiniioii and Gyrodiniuni. namely. GijnniodiuiiDU hawKhis and 

 Gjjrodi)iium viridescciis. We thus find the genus Aniphidiuiiim, previously 

 reported from beach sands by Herchnan, represented here by no less than five 

 common species. It is also suggestive in its bearing on the isolation h^-pothesis 

 that we find within this very restricted and fairly unifonn habitat, in con- 

 siderable abimdance and constantly intermingled, five species of the genus 

 Amphidi)iiu))i, and, moreover, all these appear to be closely related, if structural 

 similarity may be taken as a clue to relationship. These five species constitute 

 nearly one-third of the valid species within the genus. A common habitat is 

 no bar to speciation in this instance. It is also noteworthy that these sand beach 

 forms present a t^^De that is only rarely met with in the neritic and pelagic 

 fauna, shown by the strong dorso ventral compression of the body. 



The fresh-water species of the dinoflagellates also form another fairly 

 uniform group, more nearly related to the arenaciphilous species than to either 

 the neritic or pelagic forms. They are uniformly of a small size, with two 

 exceptions, Gijmnodinium fuscnm and G. mirahile, which more closely approxi- 

 mate the average size among the pelagic groiip. 



The fresh-water species of the G^Tiinodinioidae thus far described belong 

 to the genera Hemidinium, Amplddinium, Gymnodinium, and Gyrodiniiim. 

 Among the species of the last three genera found in this habitat there is a 

 notable lack of the more highly specialized species, as well as a complete absence 

 of the more highly developed genera of the G^Tiinodinioidae, the fresh-water 

 forms representing only the more primitive and the more generalized species 

 of the grovips. 



The non-thecate dinoflagellates are found in fresh water in all parts of the 

 globe. Most of the species described, however, have been found in the central 

 part of Europe, particularly in the waters of Switzerland and neighboring 

 countries. Complete lists of these will be given in the further discussion of 

 this subject under each genus and need not be repeated here. 



From other parts of the world the records are only fragmentary. A single 

 one comes from Eg^-^jt in the notes of Schmarda (1854), who records the pres- 

 ence of three species of Peridiniiim in the Xile Eiver and adjacent waters. 

 These are probably species of Gymnodinium. From South America the only 

 representatives of this group of which we have any records are those of 

 Gy^nnodinium fnscum and G. viride by Cunha (1913) from Brazil. 



In Xorth America a like paucity of observations on the Cx^innodinioidae is 

 foimd. Cockerell (1907-1910) noted the presence of an unidentified species of 

 Gymnodinium in the waters at Boulder, Colorado. Conn (1905) also found a 

 species of Gymnodinium in Connecticut. From Japan, Ohno (1911) has de- 

 scribed a single species, Gymnodinium hiciliatum. and from New Zealand 

 ]\Iaskell (1887) reports G. varians. Three species of Gymnodinium, G. aerugi- 

 nosiem, G. hogoriense, and G. varians, were observed by Klebs (1912) in Java. 



