GENUS HETEROMASTIX. 463 



In addition to liis institution of the new genus Dimastigoaulax for tlie reception of 

 the species last described, Diesing, /. ^., has further proposed to subdivide the flimily 

 of the Peridiniidc^ as here defined into several other subordinate genera. The 

 definitions submitted not, however, being the outcome of his personal acquaintance 

 with the organisms treated upon, but being based chiefly on the imperfect descrip- 

 tions of various earher authorities, are not considered sufficiently reliable for adoption 

 in this treatise. An estimate of Diesing's proposed innovations in this direction may 

 be gathered from the fact that a new genus, Hctcroattlax, is proposed by him for the 

 reception of the animalcules here included under the titles of Gymnodiiuuin fuscum, 

 Peridinium {Gletiodinium) incrme, and Glaiodiniiim acuDiinata. That of Gonyaulax 

 iox Ferid'miiiin sp'uiifcrum^ that of Glciioaulax for GymnodiniuDi {Glcnodiniiun) cequale, 

 and that of Proaulax for Gyiimodiniuin corpusadiim. At the same time the ordinary 

 horned and liornless representatives of the two genera Ceratiuiii and Peridinium are 

 retained under the last-named generic title, while the genus Glcnodinium is left in 

 the position originally assigned to it by Ehrenberg, the altogether unstable character 

 of the presence of an eye-like pigment-spot being cited as distinguishing it from 

 Peridinium. 



Fam. II. HETEROMASTIGID^, S. K. 



Animalcules free-swimming, bearing one vibratile and one trailing 

 flagellum, these appendages being supplemented by an adoral fringe of 

 cilia ; oral aperture distinct, anteriorly located. 



Genus I. HETEROMASTIX, J.-Clk. 



Animalcules naked, free-swimming, ovate or elongate, highly plastic and 

 changeable in form, metabolic ; flagella two in number, inserted close 

 together at the anterior extremity, one directed in advance, locomotive and 

 vibratory, utilized as a tractellum, the other one trailing in the rear 

 gubernacular or anchorate; a fringe of cilia extending on the ventral surface 

 from the point of insertion of the flagella towards the posterior extremity ; 

 endoplasm frequently enclosing a coloured eye-like pigment-spot ; oral 

 aperture situated close to the base of the two flagella. 



Heteromastix proteiformis, J.-Clk. Pl. XXIV. Figs. 70 and 71. 



Body highly contractile, changeable in form, mostly elongate fusiform 

 or lanceolate, with a more pointed anterior extremity ; flagella long and 

 stout, the anterior one, or tractellum, vibratile, about twice the length 

 of the extended body, the trailing flagellum or gubernaculum about half 

 this length ; supplementary cilia produced along a longitudinal groove 

 which extends backwards on the ventral surface from the insertion of the 

 flagella through about one-half of its entire length; a red eye-like spot 

 usually present at the anterior extremity. Length of body 1-500". 



Hab. — Fresh water. 



This remarkable form, figured and described by Professor H. James-Clark in the 

 Memoirs of the Boston Society of Natural History for the year 1868, is among the most 

 interesting representatives of the Cilio-Flagellate group. With a flexible polymorphic 

 body most closely resembling that of an Astasia or Euglena, exhibiting likewise the 

 coloured pigment-spot of the latter genus, it possesses the two differentiated flagella, 



