ANTARCTIC ROTIFERA 57 



also elliptical but was thicker shelled, and was covered with little points projecting 

 from the surface (Fig. 



Genus Diaschiza 

 Diaschiza tenuior, Gosse ? (17) (Plate XIII., Figs. 16o-16/) 



Of the species described in Dixon-Nuttall and Freeman's Monograph of the genus 

 (13) the Antarctic Diaschiza can only be D. tenuior. It differs only in being somewhat 

 laterally compressed, and in carrying the toes more ventrally than usual. The 

 length of the toes easily separate it from D. caeca, Gosse: 



With it was associated a much smaller animal, which may be the male of the same 

 species (Figs. 14c-14d). It has a large head and comparatively insignificant body. 

 The corona has the large strong cilia common to most males, and it swam powerfully. 

 The dorsal cleft is seen on the trunk. The segment between the trunk and the toes 

 is well marked. The toes are small, conical, divergent and decurved. Unlike most 

 males it possesses teeth. The male organs were not definitely seen, nor were any 

 viscera distinguished. 



In the female the seise at the base of the toes were not made out, but we were 

 working with very poor light. 



The elliptical, smooth, thin-shelled egg was seen, containing the young. A 

 smaller egg, with thick shell, through which obscure lines passed obliquely in various 

 directions (Fig. 16/), contained an animal with jaws like those of the supposed male. 



REMARKS ON THE ANTARCTIC ROTIFER FAUNA 



Its Composition. The Rotifer Fauna of Cape Royds, comprising not much more 

 than a fiftieth part of the known species, is very remarkable in its composition. When 

 the number of species is so small it is curious that all the orders of Rotifera are repre- 

 sented [the Scirtopoda being, as a result of Beauchamp's studies (2), reduced from 

 ordinal rank]. 



The great preponderance of the small order Bdelloida (with twelve species) over the 

 Plo'ima (with four species) is not surprising in view of the well-known remarkable 

 vitality and facility of distribution of these animals. 



The proportions in which the various genera of Bdelloids occur in the fauna are 

 very curious and interesting. The four species of Philodina are all unknown else- 

 where. The large genus Callidina, which elsewhere contains half, or more than half 

 of the species in the entire order, has only three species at Cape Royds. Two of these 

 are known species and one is new. The small genus Adineta, of which only seven 

 species have been described, has no fewer than five species at Cape Royds. Only one 

 of these is new to science. The genus Rotifer is absent. 



BRIT. ANTARCT. EXPED. 1907-9. VOL. I. H 



