794 PER1DINEAE OF NEW SOUTH WALES, 



dineae in my former paper "Plankton of the Sydney Water- 

 Supply" left much to be desired. They have now been carefully 

 revised, the nomenclature corrected, the types checked from the 

 original samples and better figures supplied. A source of con- 

 siderable error at that time was the expectation of finding here a 

 considerable number of European types. On the contrary, up 

 to date only two such have been recognised viz. P. Willei Huit- 

 feld-Kaas, and P. umbonatum var. inaequale Lemm. and even 

 these were not quite the same as the published types. Also, the 

 larger European forms all have areolate membranes with the 

 exception of P. Westii Lemm. in which the membrane seems to 

 be of the same character as in P. hieroglyphicum mihi. But in 

 our waters are found no less than five distinct types of membrane 

 besides, viz. granular, striolate, scalariform, ridged, and banded. 

 These give the cell such a distinct appearance that in spite of 

 some similarity in the epivalve I have not considered it reason- 

 able to arrange them under the nearest European type. There 

 are also, in almost all cases, other differences, slight perhaps but 

 well-marked and characteristic, and it seems to me unwise to 

 complicate a distinct type by the inclusion within it of another 

 type. Their connection can be much better recognised by form- 

 ing them into groups such, for instance, as (1) the P. tabulation 

 group to which P. bipes Stein and P. striolatum mihi belong; 

 (2) the P. chictum group under which fall P. Westii Lemm., P. 

 granulosum mihi and P. zonatum mihi; (3) the P. Willei group 

 including P. australe mihi and P. hieroglyphicum- mihi. There 

 will be found also, connected with each of these types ; quite a 

 number of distinct variations, partly caused by differences in 

 dimensions and partly the result of various modes of growth. 

 For example, whether the cell is angular (faceted) or rounded, 

 that is, whether the plates are concave or convex, makes a vast 

 difference to the appearance of a specimen, while at the same 

 time the arrangement of the plates may be identical. I found 

 it difficult to persuade myself to place var. guildfordense under 

 P. caudatum. 



Polymorphism. — Wider experience of the Peridineae and closer 

 study of the various forms has convinced me that the lumping 

 together of the various types is inexpedient even if it can be 

 maintained from a biological point of view. Nevertheless this 

 closer study has itself brought to light a phenomenon which 

 seems to point to polymorphism through diverging lines of de- 



