454 ORDER CILIO-FLAGELLATA, 



Ceratium delitiense, Ehr. 



Cuirass ovate or subspheroidal, with a single median, lateral, short, 

 acuminate process. Length 1-430" to 1-280". 

 Hab. — Fossil in the chalk flints of Delitzsch. 



The inclusion of this species among the representatives of the present genus, or 

 indeed, in the Protozoic sub-kingdom, is necessarily probational. 



B. Horn-like Processes as long or longer than the Body. 

 Ceratium tripos, Miill. sp. Pl. XXV. Figs. 24, n, and 36. 



Body somewhat triangular, truncate in front and tapering posteriorly, 

 the anterior segment of the cuirass bearing two long, laterally developed, 

 recurved, horn-like processes, and the posterior one a single, similarly 

 long or longer and straight median process ; the edges of these processes 

 usually more or less denticulate. Length of body, including the horns, 

 1-140" ; without the horns, 1-430". 



Hab. — Salt water. Colour yellow ; highly phosphorescent. 



This species, originally described by O. F. Miiller under the title of Cercaria 

 tripos, is subject to great individual variation, and more especially with respect 

 to the proportionate size, and angle of divergence from the body, of the horn- 

 like processes. Two of the more prominent of these variations, indeed, originally 

 received a separate specific description at the hands of Ehrenberg, under the 

 respective titles of Peridiniwn macroceros and P. arcticum. Briefly epitomized, 

 Ceratium tripos and its two leading varieties may be thus distinguished : — 



C. tripos {iiormal forni), PI. XXV. Fig. 33. — The two anterior horns much shorter 

 than the posterior one, about equal to the body in length, arched backwards in such 

 a manner that, if continued, their points would cross the hinder and median 

 process ; the margin of anterior horns finely and indistinctly denticulate. 



Var. a {P. macroceros, Ehr.), PI. XXV. Fig. 24. — All three horns very long and 

 slender, the two antero-lateral ones usually the longer, sometimes exceeding six 

 times the length of the body, produced first in advance of the body, the right one more 

 so than the left, and then curved round and continued backwards in a straight line 

 and at an angle of divergence from the posterior and terminal horn ; denticulation 

 of the margin of the two anterior processes more distinct than in the normal form. 



Var. p {P. arcticum, Ehr.), PI. XXV. Fig. 36. — Horns subequal, very thick, 

 about twice the length of the body, all three curved, strongly and uniformly denticu- 

 late ; the two antero-lateral horns not produced in advance, reflected backwards at a 

 divergent angle. 



Although, seen separately, the three above varieties would seem to lay claim to 

 separate specific recognition, it will be found that every gradation of form connecting 

 the one with the other occurs among examples from the same locality. At the 

 same time it has been observed that while the normal form of Ceratium tripos is 

 most abundant in the vicinity of Bergen, the variety a, macroceros, predominates on 

 the west coast of Norway, while the variety /?, arcticum, occurs most numerously in 

 the more northerly latitude of Spitzbergen. The eminent phosphoric properties 

 attributed to the species by Ehrenberg and Michaelis have not been confirmed by the 

 researches of Claparede and Lachmann. According to Dr. Pringsheim, a species 

 closely resembling C. tripos occurs in fresh water in the neighbourhood of Berlin. 



The author has recently received from Dr. Wm. J. Gray, F.R.M.S., a sample of 

 " surface skimmings " collected by Count Castracane in the neighbourhood of Fano, 

 in the Adriatic, that is particularly rich in Peridiniidae, Ceratiuui tripos being the most 

 abundant type, and five other forms, Ceratium fusus, Ceratium divergens, Ceratium 

 eugrammum, Prorocentrum micans, zxx^Dinophysis caudata, being more or less sparingly 



