60 H. ]\I. "WOODCOCK. 



from C. irregularis), but onglit ratlici' to bo placed in 

 different genera. As C. liolothurife is tlie type-species, this 

 form ought to retain the generic name of Cjstobia, the 

 other two species being united in a new genus, for which I 

 propose the name Diplodina. 



Relationships. — Diplodina irregularis and D. min- 

 chinii are, undoubtedly, closely allied to Gonospora, 

 G. varia, in particular, having a fundamentally similar spore. 

 On the other hand, the tailed spore of Cy stobia holothuri je 

 resembles that of one or two genera placed by Leger (19), on 

 account of that very character, in a family distinct from the 

 Gonosporidte — namely, the TJrosporidas. The affinities 

 of C. holothuria3 seem to be, in fact, with Lithocytis 

 schneideri, and, in a slightly less degree perhaps, with 

 Urospora (c f. lagidis). 



Definition. — We may thei'efore snmmarise the systematic 

 position of the parasites above discussed as follows : 



Family, Gonosporidas; genus, Diplodina (nom. nov.). 



A neogamous Gregarine of large size and regular shape, 

 parasitic in Holothurians. When in the " free " or gregarini- 

 form condition the adult couple is perfectlj^ oval in outline, 

 when encysted it is spherical. Conjugation is completely 

 isogamous. The ovoid spores have dissimilar poles, the basal 

 end being rounded, while the exospore at the opposite eud is 

 prolonged as a funnel- or cup-like expansion open to the 

 exterior. 



(1) D. i rregularis (Minch.). Association terminal (end- 

 to-end). Septum between the two members either present 

 or absent. The cysts remain attached to the Avail of the 

 blood-vessel. The size of the spoi*e averages 26 ju x 12 ^u. 

 The endospore, also, is turned outwards, as an inner funnel open 

 to the exterior, its base being closed by a cap or plug. The 

 sporozoites possess an elongated nucleus near one end. 

 Habitat: blood-vessels of H. forskali. 



(2) D. minchinii, Woodc. Association lateral. Septum 

 never present. Sporulating cysts usually occur in the con- 

 nective tissue of the body-wall or retractor muscles. The 



