210 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Irish Sea Species of Peridiuium. 



Mr. Eiddell has drawn up for us the following list, 

 with diag'iioses, of the species of Peridininm we have 

 found, so far, in our district. 



G. 3. 



Genus Peridinium. — Testa divided into plates; 

 preciiigular plates seven, bottom plates Iavo. 

 Sub-genus I. — Protoperidinium : Girdle nearer apex on 



right side ; usually no antapical horns ; spines may 



be present. 



(1) P. orhicvhu-e, Paulsen; globtihu', small; no 



spines and no apical hoin ; giidle almost equa- 

 torial. L. 0"04 — 0045 mm. Rare in Irish Sea. 

 (See fig. :], No. I.) 



(2) P. (> rat mil, Pouchet ; depressed; apical horn 

 not prominent ; two anta])ical spines. L. 0062 

 mm., greatest breadth 0084 mm. Not un- 

 common. (Fig. '], No. 2.) 



(3) P. sfeini, Jorg. : pyrifoini ; apical horn distinct; 



two antapical spines, each winged. 1j. 0045- 

 0-052 mm. Rare. (Fig. 3, No. ;J.) 



