i8o 
F. Cavers. 
The remaining Peridiniales are placed by Schiitt in the family 
Peridiniaceae, in which the shell differs from that of the Proro- 
centraceae in having a series of girdle plates intercalated between 
the two valves. The girdle consists essentially of a narrow ring¬ 
like plate with a groove (annulus) for the transverse flagellum, and 
a pair of plates (sometimes each divided into several plates) placed 
at right angles to this and containing the longitudinal groove (sulcus). 
Each valve consists of two or more polar plates, which are either 
joined directly to the girdle series or are separated by intercalary 
Fig. 8. Prorocentraceas.— 1, 2, Haplodinium antjoliense Klebs : 1, surface 
view ; 2, side view ; 3, Cenchridimn globosum (Williams) Stein. 4, 5, Amphidinium 
operculatum Clap, et Lach. ; 4, ventral view, showing the flagella; 5, dorsal 
view, showing nucleus and chromatophores. 6 to 10, Exuvicella marina Cienk. : 
6 and 7, two aspects at right angles to each other, showing the flagella and 
the surface markings of the shell ; 8 and 9, optical sections corresponding 
respectively with 6 and 7, and showing the nucleus, chromatophores, pyrenoids, 
and contractile vacuoles ; 10, empty valves of the shell, after escape of encysted 
contents. 11 and 12, rrorocentvum micans Ehrb., two views at right angles. 
Chr., chromatophore ; c.v., contractile vacuole; nu., nucleus ; \pyr., pyrenoid. 
1, 2, 8, 9, 10, from Klebs ; 3, 4, 5, from Stein ; 6, 1, 11, 12, from Schiitt. 
All somewhat diagrammatic. 
plates. The upper valve (epitheca) bears an apical pore, and in 
most cases the sulcus is confined to the lower valve (hypotheca), 
though sometimes it extends beyond the annulus right to the apex 
of the cell ( Steiniella , Gonyaulax), or it may be short and extend 
equidistantly on either side of the annulus ( Protoceratium ). Schiitt 
divides the Peridiniaceae into four sub-families—Glenodinieae (only 
genus Glenodinium) ; Ptychodisceae (only genus Ptychodiscus ); 
Dinophyseae (six genera, including the most bizarre forms of 
