OF THE PEliIDmiJ<:A. 



07/ 



P. uberrimum (Allman). Nearly sphe- 

 rical ; coloiu' reddish-brown ; nucleus 

 well-defined, central. A secondary fur- 

 row springs vertically from the annidar 

 one, and terminates at the pole. A 

 stigma usually present at the polar ex- 

 tremity of the vertical furrow. S^^dms 



b. PericUnia with horns 



P. (Ceratium) (?) pyrophoi'um. — 

 Ovate, spherical, with two little elevated 

 points at its anterior extremity. It is 

 very delicately areolate and gi-anular. 

 Fossil in the flints of the chalk forma- 

 tion at Berlin. 1-570' to 1-480". 



P. (Ceratium) (?) Belitieme. — Ovate, 

 spherical; with a little stiff point near 

 the middle laterally. Fossil in the flints 

 ofDelitzsch. 1-430" to 1-280". These 

 two supposed fossil Peridmia and the 

 Ch(etotifphIa (?) pyritce appear rather to 

 be sporongia of Algse. 



P. (Ceratium) acuminatum. — ^Brown- 

 ish-yeUow; ovate, spherical, slightly 

 three-lobed, and having a little pro- 

 cess at the posterior end. '' I observed j 

 this species/' says Ehrenberg, " in phos- | 

 phorescent sea-water from Kiel, and it is I 

 veiy probable that the light proceeded 

 from this animalcule. It is the smallest i 

 phosphorescent sea animalcule that is 

 bio^vTi." 1-600" to 1-570". 



P. (CERATirM) cornutum (Pursana 

 Himndinella, M. ; Ceratium Hirundinella, 

 Duj. and Perty). — Greenish ; not lumi- 

 nous; rhomboidal and rough, with one, 

 two, or three straight horn-like processes 

 in front, and a single one (often curved) 

 posteriorly. 1-280" to 1-140". 



Perty asserts that Ehrenberg has re- 

 versed this animalcule in his account 

 and illustrations, as he has likewise done 

 in other species of this genus ; for it is 

 the single horn which advances fore- 

 most, and indicates the anterior extre- 

 mity. The same author, moreover, 

 states that in the majority of speci- 

 mens one or more red specks are to be 

 found, generally in the posterior half, 

 near the middle line between the large 

 and small homs. 



P. (Ceratium) TriiJOs ( Cer carta Tripos, 

 M.). — Yellow, brilliantly phosphores- 

 cent; urceolate, broadly concave, smooth, 

 and three-horned ; the't^-o frontal horns 

 very long and recurved ; the third, or pos- 

 terior one, straight. Ehrenberg says, 

 ". "^^^ 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 in 

 each nothino- else besides a sinele animal- 



actively by the aid of its flabeHum, and 

 of cilia generally disposed on the surface, 

 and not confined to the fuiTOws as Ehr- 

 enberg represents. Occm-s in a quies- 

 cent state. 1-1000" to 1-500". Ponds, 

 Phoenix Park, Dublin. 



— Subgenus Ceratium. 



cule 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, x. 219, 220, repre- 

 sent an under and side view. In the sea, 

 near Copenhagen andKiel. 1-140"; with- 

 out the horns^ 1-430". 



P. (Ceratium) Michaelis. — Colour 

 yellow ; intenseh' phosphorescent. Lo- 

 rica ovate and smooth, with three short, 

 straight horns, as shown in fig. 221. A 

 flagellum is not visible. In phosphores- 

 cent sea-water. 1-570". Named after 

 Dr. Michaelis, its discoverer. 



^ P. (Ceratium) Fusus (x. 222, 223).— 

 Yellow, intensely phosphorescent; ovate, 

 oblong, and smooth. The two horns are 

 straight and extended in opposite direc- 

 tions, producing a fusiform fig-ure. Ehr- 

 enberg states that he has seen the cilia 

 of the furrowed zone, and the single fila- 

 ment when at rest ; also an opening or 

 mouth in the lorica, near the insertion 

 of the filament. With horns, 1-120" to 

 1-90". 



P. (Ceratium) Ftirca. — Yellow, very 

 phosphorescent; urceolate, TN-ith three 

 horns ; two in front short, in the form of 

 a fork; one behind longer. In phos- 

 phorescent water, at Kiel. 1-120". 



P. (Ceratium) divergens. — Y^ellow; 

 cordate-ovate, smooth ; with two diver- 

 gent frontal acute spines, dentate at the 

 base ; posterior portion attenuated, look- 

 ing as if shortly homed. Diam. 1-576". 

 In the Baltic. 



P. (Ceratium) macroceros. — Yellow; 

 habit of P. Triptos, but more slender, and 

 with longer horns, which are four times 

 the length of the body. 1-216". In 

 the Baltic. 



P. Tridens. — YeUow, with the habit 

 oi P.Jlarum, P. divergens, and of P. Mi- 

 chaelis; surface granular, with three acute 

 frontal horns, and its posterior portion 

 attenuate. 1-576". In the Baltic. 



P. (Ceratium) macroceras (Schrank) 

 or C longicortie (Perty) is mentioned by 

 Perty, and does not appear quite equiva- 

 lent to C. macroceros, to which its name 

 is too much alike. It is the largest of 

 2 p 



