264 E. A. ANDREWS. 



deep, since its attached face is flattened out against the support, 

 while the free face or back is very convex. The posterior blind 

 end is bluntly rounded and affords attachment for the foot end 

 of the animal. The tube rises at about 45 degrees from the 

 axis of the sac or the plane of attachment, and ends in a freely 

 open mouth without valves but with a reflexed lip. As a rule 

 about six turns of a spiral-ridge pass about the tube, but the 

 number is not fixed. The spiral seen from the right side, Fig. I, 

 passes toward the top of the tube over the dorsal side. The 

 nature and mode of formation of the case and the spiral of the 

 tube will be described elsewhere. 



AREAL AND DEPTH DISTRIBUTION IN THE SEVERN. 



First seen on the leaves of Elodea (Anacharis}, the cases or 

 bottles of these animals seemed to the eye mere dark lines | mm. 

 long that might be excrement of some small snail lying abundantly 

 on the leaf amidst sediment. 



But the microscope reveals marvelous greenish, transparent, 

 bottle-like cases containing a clear, but blue-green animal that 

 shyly withdraws till no longer disturbed and then may, from time 

 to time protrude from the mouth of the bottle as a slender 

 thread divided like a snake's tongue into two forks, which are 

 held curved or else bent about and waved till all suddenly 

 vanishes as a mere lump within the bottle. The animal might 

 be compared to a miniature fork with long bent arms all made of 

 glass but more pliant and elastic than rubber. 



The cases with or without the contained animal were found on 

 the leaves of several plants, chiefly Elodea and Potamogeton 

 growing upon the bottom of this decidedly saline water, and also 

 upon floating leaves and stems of these plants in the open river 

 as well as on the sides of a boat and on wood. These plants 

 form zones along the shores of most of the side branches of the 

 river, known as "creeks"; the Potamogeton zone is nearer shore 

 and grows in water one to two feet deep ; the Elodea appears as a 

 blue-green zone some twelve feet wide in water two to six feet 

 deep, at high tide (the water falling one to two feet). FoUicnUna 

 was taken from "Back Creek" below Annapolis up beyond the 

 "White Sands," some nine miles, in side creeps on both shores. 



