56 JAMES MURRAY 



perfectly, but remaining so still that it could easily be photographed while living and 

 feeding. 



Hydatina was only seen in Coast Lake. Its restriction to one lake led Mr. 

 Rousselet to suggest the possibilit} r of its recent introduction, say by the Discovery 

 Expedition. It is not impossible, though hardly probable. Hydatina is a common 

 animal in ponds around farmhouses, and eggs might readily enough adhere to farm 

 produce such as hay or straw. When Captain Scott and Dr. Wilson camped for a 

 short time at Cape Koyds, close by the spot where we afterwards had our hut, they 

 may have had some straw packing among their gear. In this connection it is worth 

 noting that we dredged in Back-door Bay a stalk of old sodden straw on which a 

 sponge had grown. This straw could hardly be of older date than the Discovery 

 Expedition. Against the theory of the recent origin of Hydatina is the fact that 

 Coast Lake is a mile from Captain Scott's camp, and that several suitable lakes lie 

 nearer the camp. Still, one egg is enough for the introduction, and the straw bear- 

 ing the one egg may have blown to Coast Lake. 



Family NOTOMMATAD^E 



Genus Pleurotrocha 

 Pleurotrocha, sp. ? (Plate XIII. , Figs. 14a-14c) 



Description. Of large size, 520 yu in length. In lateral view greatly elevated 

 just behind the middle of the trunk. Head long, mouth narrow. Jaws very like 

 those of P. grandis, Western, and some related species. Toes longer than those of 

 P. grandis. Stomach large, orange-coloured. 



This large active animal was found in Blue Lake early in the season, before the 

 requisites for narcotising and preserving were available. It was fairly abundant then 

 but was not obtainable afterwards, when it could have been photographed and pre- 

 served. We are therefore dependent for our knowledge of the animal on a few 

 sketches by onelittle acquainted with the order to which it belongs. Mr. Rousselet 

 has examined the sketches critically, taking such points as could be best trusted, and 

 compared them with the same points in the species coming nearest to our one. 



It is undoubtedly very near P. grandis (41), which is like it in size and activity. 

 The jaws differ in being more ovoid in form, diminishing backward from the widest 

 part. In P. grandis the greatest width is maintained for some distance backward. 

 The toes are considerably longer and narrower than in P. grandis. The general 

 outline of the jaws is very similar to that of Diglena permollis, Gosse (16), as shown 

 in a drawing by Mr. Dixon-Nuttall. 



Reproduction. Two kinds of egg have been seen which contained animals having 

 jaws exactly like those of the Pleurotrocha (the drawing, Fig. 14c, is made from an 

 example in an egg). One of the eggs was elliptical and smooth. The other was 



