THE MAST1GOPHORA 185 



B. Annulus spiral with a single pitch, sulcus slightly (Spirodinium) 

 or markedly (Pouchetia) spiral, decussating the annulus at both ends. 

 The transverse flagellum arises at the anterior end of the annular spire, 

 the longitudinal flagellum at the posterior end of the sulcar spire. 



Spirodinium, Schutt ; Cochlodinium, Schutt ; Pouchetia, Schu'tt. All 

 marine. 



Pouchetia resembles Cochlodiniunt, but is distinguished by the 

 possession of a complicated stigmatic apparatus consisting of a red or 

 black pigmented body with one or more large refractive lens-like 

 spherules adjoining it. 



The interesting genus Polykrikos, Btitschli, consists of two, four, or 

 rarely eight individuals united together into a colonial organisation 

 (Kofoid [10a]). It is also peculiar in the possession of nettling organs, 

 and is said to present holozoic nutrition. Coasts of Europe and California. 



All Gymnodiniaceae may be naked or enclosed temporarily in a 

 gelatinous membrane. The tribe includes marine and freshwater species. 



TRIBE 2. PROROCENTRACEAE. 



Carapace bivalve, perforated with numerous pores, without annular 

 plates and without annulus, the two halves meeting directly like the 

 edges of two opposed watch-glasses; longitudinal flagellum has the 

 character of a tractellum with the transverse flagellum vibrating about 

 its base ; chromatophores yellow ; contractile vacuoles represented by 

 pusulae opening into the groove from which the flagella arise at the 

 ^interior end of the cell-body. 



At the time of division each daughter-cell receives one parent valve 

 and forms the other anew. The Prorocentraceae are entirely marine. 



Lotsy (12) regards this tribe as being probably similar in some respects 

 to the ancestors of the Diatomaceae. 



Exuviaella, Cienkowski, rounded in front and behind. Prorocentrum, 

 Ehrenberg, heart-shaped, flattened, pointed behind, with rostral prolonga- 

 tion of one of the valves at the anterior or flagellar end. 



TRIBE 3. PERIDIXIACEAE. 



These are characterised by the possession of a multitabulate cellulose 

 .carapace or cuirass, each valve being composed of at least two plates 

 which are frequently areolated, and, in addition, there are three or more 

 mmular and sulcar plates. The longitudinal flagellum plies in the 

 sulcus ; the transverse flagellum arises at the junction of sulcus and 

 annulus and vibrates in the latter groove (Fig. 12). 



The cellulose membrane which constitutes the carapace or cell-wall 

 of the Peridiniaceae is perforated by minute pores and is generally 

 provided with processes which may take the form of horns, spines, or 

 aliform expansions. 



Multiplication takes place by oblique longitudinal (rarely transverse) 

 division, each daughter-cell receiving half of the parent carapace, that is 

 to say, half of each valve, and regenerating the other half. Resting 

 : sporocysts are enclosed in a gelatinous membrane, and it may be noted 



