10 MABINE INFUSORIA. 



oeoua skimmings. The lorioa is of glass-like transparency, sub-cylin- 

 drical, and produced at the proximal or posterior extremity into an acute 

 and often much attenuated spine-like point ; it bears, in fact, no 

 inconsiderable resemblance to the segment of a frustule of the diatom, 

 Rhizosolenia setigera, with which it is so abundantly associated. The 

 contained animalcule, resembling an elongate Vorticella, is fixed by a 

 contractile pedicle to the bottom, or sometimes to one side of the lorica, 

 and does not project beyond its anterior naargin. The oral cilia, forming 

 a spiral wi'eath at the distal extremity, are exceedingly long and 

 powerful, and in its normally free-swimming state serve to propel the 

 animalcule and its associated lorica backwards through the water with 

 great rapidity. According to Claperede and Lachmaun, the entire body 

 in the representatives of this same genus is clothed throughout with fine 

 vibratile cilia, and thus assimilates the typical characteristics of the 

 section Heterotricha ; the presence of these finer cilia, however, could 

 not be detected in the spirit-preserved example recently examined. 



3. — Ceratium fusus, Ehr., (Plate TV., Fig. 4.) — Several examples of 

 this cilio-flagellate type have been found scattered through the prepared 

 slides referred to, this species being remarkable among its associated 

 family group of the Peridiniidse on account of the production of the two 

 segments of the carapace into single attenuate axial prolongations, the 

 other representatives of the same genus, as C. tripos and C. furca, 

 having usually two antero-lateral and not axially disposed processes. 

 Although Ceratium is usually regarded as an essentially marine type, one 

 form, C. Kumaonense, has been described by Mr. Carter (Ann. Nat. Hist., 

 Vol. VII., 1871,) as occurring in prodigious numbers in the lakes of 

 Kumaon, Hindostau, at an elevation of fi-om 4,000ft. to 6,500ft. above 

 the sea level, while the Ceratium (Peridinium) longicorne of Perty, 

 (havmg, like C. Kumaonense, tlu'ee anterior horn-like prolongations,) 

 originally found in Switzerland, has been recently encountered in the 

 neit'hbourhood of Birmingham, whence I have received speci- 

 mens for identification from the hands of Mr. Levick. Among the 

 Falmouth specimens of Ceratium fusus, one exsunple in which the cara- 

 pace had been crushed, and the enclosed yellowish and granular proto- 

 plasm extruded, exhibited a well marked oval nucleus-like body, 

 while the aspect of the fractured edges of the carapace seemed entirely 

 to support the suggestion recently made to me by Mr. Charles Stewart, 

 F.L.S., and arrived at by his burning C. tripos on platinum over a spirit 

 lamp without the destruction of the carapace, that this latter, in the 

 case at least of the marine types, is probably of a silicious nature. The 

 animalcule of Ceratium corresponds essentially with that ot Peridiniuvi, 

 having a monadiform structure, and single long lash-like flagellum, which 

 projects from a medially situated oval aperture ; the carapace consists of 

 an anterior and posterior valve, closely approximated, with an equatorial 

 gi'oove or channel between them upon which a circlet of fine vibratile ciha 

 is developed, and upon the ventral face of which groove the oral apei-ture 

 with its associated lash-hke flagellum debouches. The fresh-water 

 Peridinium tabulatum recently supphed to me from the neighbourhood of 



