THE MASTIGOPHORA 187 



valves with an annulus between them. Glenodinium pulvisculus, Ehrb. 

 (Fig. 10 (3 and 4)). 



FAMILY 2. PTYCHODISCIDAE. Body lens- shaped, valves perforate, 

 annulus soft, membranous. Ptychodiscns nocticula, Stein. 



FAMILY 3. CERATIIDAE. The typical genera are the well-known 

 forms of Ceratium and Peridinium. The valves of the cuirass are described 

 as the epitheca and the hypotheca respectively. The former carries the 

 apical pore and the latter the sulcus. But the sulcus sometimes extends 

 beyond its decussation with the annulus up the ventral side of the 

 epitheca to the apex of the cell, e.g. in Steiniella, Schiitt, and Gonyaulax, 

 Diesing ; or the sulcus may be short, extending equidistantly on either 

 side of the annulus as in Protoceratium, Bergh. 



In the genus Ceratium we meet with two-, three-, four-, and five- 

 horned varieties. The chromatophores of the freshwater species of the 

 genus are green, of the marine species yellowish to brownish in colour. 



Some Ceratiidae are spherical, as Blepharocysta, Ehrb., in which the 

 annulus and sulcus are only indicated by the arrangement of the plates. 

 Closely allied to Blepharocysta is the genus Podolampas, St., which has a 

 peridinioid form of body though a different tabulation. Others are 

 fusiform like the remarkable genus Oxytoxum, Stein. In Ceratocorys 

 horrida, Stein (Fig. 10 (9)), the borders of the annulus are expanded like 

 the rim of a hat, while the left sulcar margin is expanded into a wing 

 bearing long plumose spines. Pyrophacus is an oyster-shaped Ceratian 

 in which sporulation has been observed by Schiitt. The new genera 

 Heterodinium, Murrayella, Acanthodinium have recently been described by 

 Kofoid. 



FAMILY 4. DINOPHYSIDAE. The shell is divided by a sagittal suture 

 into two lateral subequal portions. The epitheca is flattened and much 

 smaller than the hypotheca. The borders of the annulus are funnel- 

 shaped, and minute brown-coloured corpuscles called Phaeosomata often 

 occur in the space between the two superimposed funnels. The right 

 sulcar border is inconspicuous, but the left border may be monstrously 

 developed into wings and spines (e.g. Ornithocercus, Fig. 10 (8)). 



In Amphisolenia (Fig. 10 (7)) the epitheca is excessively reduced, consist- 

 ing of two minute plates united together by a sagittal suture. The dis- 

 proportionately large hypotheca in this genus consists of two elongated 

 plates likewise united by a sagittal suture. The sulcus of Amphisolenia 

 (Fig. 10 (7)) proceeds from the subterminal annulus along the neck of the 

 cell for a distance equal to about one-quarter of the length of the body, 

 terminating at a rather deep pit, representing the depression from which 

 the nagella arise in other forms. This depression may be conveniently 

 distinguished by the term flagellar fundus or simply the fundus. 1 



In Amphisolenia the protoplasmic contents of the cuirass consist of 

 a nucleus, a moniliform chromatin reticulum, and several ellipsoidal 

 plasmosomes of amyloid character. A pusule situated near the nucleus 

 opens by a slender canal into the flagellar pore, and one or more accessory 

 pusules may lie near it in the cytoplasm. 



1 The German term is " Gcisselspalte." It is not a true pharyngeal pit although 

 it strongly resembles one. 



