FAUNA OF THE CHESS AND GADE. 203 



at Langleybury Pool (elevation above sea-level about 200 ft.), 

 Berkhamsted Castle moats (about 300 ft.), and Parsonage Farm 

 Pool, Abbots Langiey (about 400 ft.), the numbers of specimens 

 obtained have been very large ; on the other hand, at Wigginton 

 Pool (700 ft.), among the Chilterns, the numbers obtained have 

 not been nearly as large as in the pools before mentioned. 

 Again, at many places close to the Chess, the Gade, the Bul- 

 bourne, and the canal, are extensive watercress-beds, through 

 which the river or canal waters are diverted. Some parts of 

 these beds have been much less disturbed than the rest, and 

 contain, besides watercress, small quantities of starwort and 

 duckweed. In these parts only comparatively small numbers 

 of specimens of S. mucronata are usually found. 



Often when seen beneath the microscope the specimens of 

 S. mucronata swam about quite freely and rather rapidly, but if 

 the water on the slide contained some vegetable matter, they 

 usually spent their time by moving about this. Their long toes, 

 resembling the blades of ancient Boman gladii, were frequently 

 swung forwards so as to be almost parallel to the long axes of 

 their bodies. The comparatively large, bright red cervical eye- 

 spot was always easily seen. 



2. Pterodina patina, Ehren. — Most of the specimens of this 

 Botifer were obtained from Langleybury Pool, the rest being chiefly 

 from Parsonage Farm Pool, Abbots Langiey, and Berkhamsted 

 Castle moats. All those examined were taken during the spring 

 and summer months. Very many samples of water from Par- 

 sonage Farm Pool were taken nearly every month during 1912 

 and 1913. Not a single specimen of P. patina was seen in the 

 1912 samples, but several specimens were obtained in March 

 and August of 1913. 



The specimens from Langleybury Pool were exceedingly 

 numerous in May and June, 1913. Most of them showed a few 

 bosses, but indistinctly. These Pterodinas usually glided slowly 

 through the water, occasionally turning their edges to view, 

 when they presented a comic resemblance to a broken-down 

 pedlar carrying a load on his back. When gliding through the 

 water with their dorsal surfaces exposed to view, the trunk-like 

 foot was almost always out of sight, by reason of its being 

 extended downwards to allow the setae at its extremity to touch 



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