GENUS MELODINIUM. 445 



GENUS III. MELODINIUM, S. K. 

 (Greek, melon, a peach ; dine, a vortex.) 



Animalcules naked, persistent in form but not encuirassed, having a 

 central equatorial ciliated groove, and a second shorter longitudinal furrow- 

 extending from the transverse one towards the apical extremity ; flagellum 

 single, issuing from a depression in the ventral groove ; entire surface of the 

 body ciliated, as well as the annular furrow ; coloured stigma present or 

 absent. 



This new genus is provisionally established for the reception of the Peridiniutn 

 uberrimum of Professor Allman, characterized by the distribution of vibratile cilia 

 throughout the whole extent of its cuticular surface, and by the consequent absence of 

 an indurated carapace or cuirass. It is at the same time not altogether impossible 

 that future investigation may demonstrate this animalcule to be a shell-less develop- 

 mental condition of certain ordinary Peridinia, Claparede and Lachmann having 

 shown that a shell-less or non-encuirassed state is common to the earlier phases of 

 many of these latter. In the interim, nevertheless, it appears to be desirable to 

 institute an independent generic name for a type whose characters differ so widely 

 from those of the genus with which it has been hitherto associated. 



Melodinium uberrimum, Allman sp. PL. XXV. FIGS. 34 AND 35. 



Body subspheroidal, having a transverse annular furrow and a supple- 

 mentary vertical groove developed oji the ventral surface, which extends 

 from the centre of the annular furrow to the apical extremity ; entire 

 cuticular surface finely ciliate ; endoplast conspicuous, ovate, subcentral ; a 

 red eye-like pigment-spot usually present in the apical region. Length 

 l-iooo" to 1-500"; colour reddish brown. 



HAB. Fresh water, ponds in the Phoenix Park, Dublin ; gregarious. 



As already notified, this species is synonymous with the Peridinium uberrimum of 

 Professor Allman, first described in the ' Quarterly Journal of Microscopical Science,' 

 p. 21, for the year 1855. In its broader details it would seem to correspond closely 

 with the animalcule figured and described by Claparede and Lachmann (See PL XXV. 

 Fig. 5) as a possible shell-less or transitional condition of an ordinary Peridinium, such 

 as P. tabulatiim. At the same time no trace of an entire ciliary clothing is mentioned 

 or figured by these writers, but which may nevertheless have been too fine to attract 

 notice with the magnifying power employed. 



Some estimate of the essentially gregarious habits of this animalcule may be 

 arrived at in connection with the following abstract of Professor Allman's original 

 record. Speaking at the Dublin Academy, in June 1854, he remarked, that for the 

 three previous weeks the brown colour assumed by the water in the large ponds in 

 the Phoenix Park was owing to the presence of prodigious numbers of a species of 

 Peridinium, this colour being sometimes uniformly diffused through the water, and at 

 others being collected in dense clouds varying from a few to upwards of one hundred 

 square yards in extent. Later on, the coloration of the ponds brought about by 

 the agency of these minute organisms had much increased in density ; by the Qth of 

 July the water was so deep a brown that a white disc, half an inch in diameter, was 

 invisible when plunged to a depth of from three to six inches, while a copious 

 exit stream, constantly flowing away from the ponds, presented a similar deep brown 

 hue. In many places the animalcules had descended from the surface, and were 

 found congregated in immense masses near the bottom of the water; in these 

 instances they had, for the most part, assumed a quiescent or encysted state, the 



