JFeridinaea.] iNPrsoRiAt animalcules. 517 



Duj.) — Colour greenish ; it is not luminous ; its rhomboidal rough 

 lorica has one, two, or three sti'aight horn-like processes in front, 

 and a single one (often curved) posteriorly. Length 1 -280th. to 

 1-1 40th. 



Peeidinicm tripos ( Cercaria tripos, M. Ceratium tripos, Duj.) — Colour 

 yellow; veryhriUiantin the night (phosphorescent). Lorica urceolate, 

 broadly concave, smooth, and three-horned ; the two frontal horns 

 very long and recurved, the third, or posterior one straight. Ehren- 

 berg says, " The power of this creature to evolve light is placed 

 beyond all doubt, as I took up nine phosphorescent drops, one after 

 the other, from the water, and I saw nothing else in each than a 

 single animalcule of this species." It is rigid, and swims with a 

 vacillating rolling motion upon the longitudinal axis. The length of 

 the horns is not constant, sometimes being scarcely so long as the 

 body; at other times much longer. Figs, 219 and 220 represent an 

 under and side view. Found in the sea, near Copenhagen and Kiel. 

 Length l-140th. ; without the horns, l-430th. 



P. MichaeUs. — Was discovered by Dr. Michaelis ; it is of a yellow 

 colour, and intensely phosphorescent. The lorica is ovate, and 

 smooth, with tliree short, straight horns, as shewn in fig. 221. A 

 proboscis is not visible. Found in phosphorescent sea-water. Length 

 1-5 70th. 



p. fusus. Ceratium fusus (Duj.) — Is of a yellow colour ; intensely 

 phosphorescent, and brilliant at night. Lorica ovate, oblong, and 

 smooth. The two horns are straight and opposed, giving the creature 

 the form of a spindle, as shewn at figs. 222 and 223; in the latter 

 the proboscis is in the usual vibrating state, Ehi-enberg states that 

 he has seen the cilia of the furrowed zone, and the single proboscis 

 when at rest; also an opening or mouth in the lorica, near the insertion 

 of the proboscis. Length, with horns, l-120th. to l-90th. 



P. furca. — Is of a yellow colour, and very phosphorescent ; lorica 

 urceolate with three horns ; two in front short, and in the foi-m of a 

 fork; the posterior longer. Found in phosphorescent water, at Kiel. 

 Length 1-1 20th. 



P. divergens. — Yellow ; lorica cordate-ovate, smooth ; with, 

 two divergent frontal acute spines, dentate at the base ; posterior 



