FRESH- WATER RHIZOPODS OF NANTUCKFr 



JOSEPH 



CUSHMAN 



During the spring of 1905 collections were made from the bodies 

 of fresh water on the island of Nantucket, Mass., by several mem- 

 bers of the Nantucket Maria Mitchell Association. This material 

 was turned over to me for examination. A portion of it was made 

 up of the sediment squeezed from submerged sphagnum. This, 

 as was to be expected, seemed to be the richest in Rhizopods and 

 contained many more species and individuals than the material 

 from the bottom of the larger ponds. Certain species seem to be 

 very limited in their distribution on the island, often occurring in 

 but one of the collections out of the fifty or more examined. In 

 such cases, however, there was usually an abundance of specimens 

 of the species in that one collection. Other forms which were to 

 be expected here were not met with at all. Of these Hyalosphenia 

 was the most striking genus, as it usually occurs in just such 

 material. Nearly all of the species found were of small size 

 for their respective species and may be compared with the speci- 

 mens noted by the writer and Mr. Henderson from the alpine 

 region of the White Mountains (Amer. Nat., vol. 39, March, 

 1905, p. 155 ). The cause of this minimum size in the case of the 

 Nantucket specimens is hard to explain unless for some reason 

 there is not sufficient nourishment for them, but this does not 



The following species were found: — 



1. Arcella vulgaris Ehrenberg. Breadth 52-55 n; height 21- 

 23//; aperture 12-14 /(. 



Common. Hummock and Gibb's Ponds and from bog moss. 



2. Arcella discoides Ehrenberg. Breadth 4C)-75 height 20- 

 25//; aperture 8-19 //. 



Common, but of small size. Hummock and Sc-jk ha Wnul^ and 

 from sphagnum in different parts of the islaiuh 



3. Centropyxis aculeata Stein. Breadth (m-72 /!; height 

 30-38 //; aperture 11.5-18 a. 



plied with minute alga-. esptMially « 

 certain of the records I am iiidehted 



371 



