446 ORDER CILIO-FLAGELLATA. 



flagellum and cilia having disappeared, and the body being contracted within the 

 centre of an external hyaline envelope. Multiplication by transverse fission, as 

 represented at PI. XXV. Fig. 35, is the only mode of reproduction that was 

 observed by Professor Allman, though doubtless the encysted state, in common with 

 that of all ordinary Flagellata — see also Peridinium sanguineiim — is accompanied by 

 the breaking up of the body into sporular elemeiitts. 



Genus IV. GLENODINIUM, Ehrenberg. 



Animalcules free-swimming, encuirassed, body separated by a transverse 

 or equatorial ciliated furrow into two equal or subequal portions, a more or 

 less conspicuous non-ciliated groove produced from the ventral aspect 

 of the equatorial furrow towards the apical extremity ; cuirass consisting of 

 two equal or subequal segments, which invest and correspond with the 

 anterior and posterior halves of the body, leaving bare the equatorial and 

 longitudinal grooves, not further subdivided into polygonal facets ; oral 

 aperture and insertion of the flagellum located on the ventral aspect near the 

 junction of the two grooves ; endoplasm often, but not invariably, enclosing 

 a coloured eye-like pigment-spot. Inhabiting salt and fresh water. 



As first instituted by Ehrenberg, this genus was made to include all those forms 

 of Peridinium and its allies that were distinguished by the possession of an eye-like 

 pigment-spot. As shown, however, by Claparede and Lachmann, and other recent 

 observers, this proposed feature of distinction is, as in the genus Eiigkna, inconstant 

 even among representatives of the same species, and cannot therefore be made the 

 basis of generic diagnosis. Quite recently, however, Stein * has pointed out that 

 among the animalcules referred to the genus Glciwdinium by the authority first-named, 

 there occurs one, G. cinctum, which differs from all its co-associated types in the 

 smooth . and undivided character of the two segments of the cuirass, and that this 

 distinctive characteristic is likewise shared by other animalcules previously rele- 

 gated to the genus Peridinium. For these he proposes collectively to retain the 

 generic name of Glenodinium, introduced by Ehrenberg, and it is with a similar 

 significance included in this volume. 



Glenodinium cinctum, Ehr. Pl. XXV. Figs. 27-29. 

 Body ovate or elliptical, about twice as long as broad, entirely smooth 

 and homogeneous ; cuirass composed of two even anterior and posterior 

 segments only, and not of separate plates or facets ; a red eye-like pigment- 

 spot present or absent, when developed large and crescentic, subcentral ; 

 colour light brown. Length 1-570". Hab.— Fresh water. 



This species is identical with the Glenodinium cinctum of Ehrenberg, but not with 

 the Peridinitim cinctum of that same authority ; this latter form, as presently explained, 

 representing examples only of P. tahulatum, in which an eye-like pigment-spot is 

 conspicuously developed. The encysted state of this animalcule has been observed 

 by Claparede and Lachmann, a condition of the same, with the valves of the cuirass 

 falling asunder, being delineated at PI. XXV. Fig. 29. 



Glenodinium acuminatum, Ehr. Pl. XXV. Figs. 21 and 22. 

 Body ovate or spheroidal, slightly trilobate ; cuirass smooth, terminating 

 posteriorly in a short acuminate point ; colour brownish yellow. Length 

 1-570". Hab. — Salt water, highly phosphorescent. 



* ' Infusionsthiere,' Abth. iii., 1878. 



