STAURA STRUM. 153 



Split rock Pond, Passaic Co., N. J. 



Our species differs somewhat from the typical Norwegian 

 form, but I adopt the name for our variety. 



ST. SUBARCUATUM, Wolle. Plate LVII, figs. 15, 16. 



This species is allied to the preceding, St. arcwtum; I have 

 separated it because it is smaller, the aculei at the terminal 

 angles are not so long and the marginal granules are only 

 rarely bifid. In end view, the papilla-like granules are 

 arranged concentrically, often protruding on the margins. 



Since naming this desniid, three years since, I came across 

 varieties of St. Avicula coarsely granulate, which are very 

 near to this form. A variety of Avicula would have been 

 equally appropriate. 



ST. ORESCENTUM, Hast. Plate XLI1, figs. 8-11. 



Semi-cells subelliptic, or somewhat hexagonal, base trun- 

 cate convex, undulate ; superior lateral margins each with 

 three teeth or verrucae, the upper two truncate; apex trun- 

 cate undulate; each lateral angle furnished with two, or 

 rarely three, diverging aculei, rarely unarmed ; end view 

 triangular, sides sinuous concave, sometimes furnished with 

 a subulate spine near the angles ; angles suddenly attenuate, 

 rounded and usually furnished with two, sometimes three 

 aculei, rarely unarmed ; center of triangle smooth, sur- 

 rounded by three pairs of crescentric teeth in a wide circle, 

 these are surrounded by others, so that each limb of the 

 triangle bears five crescentric teeth, two, two and one, all 

 within the margin, the last one sometimes indistinct or ob- 

 solete. 



Diameter, without aculei, 45-50 yw. 



From a small pond, Dover, N. H. 



This at first view recalls 8t. arcuatum, also St. forficula- 

 tum, but in end view the crescentric markings, the suddenly 

 attenuate angles ; the sinuous concave sides and the lateral 

 subulate spines make a good specific character. 



SECTION III. 



MEMBRANE PILOSE, SPINOUS OR ACULEATED. 



ST. ACULEATUM, Ehrb. Plate LVI, figs. 1, 2, 3. 



Cells spiuulose; semi-cells with sides somewhat drawn out, 

 margined with smaller aculei, and terminated by larger ones; 

 end view usually with three, but sometimes also with four 

 angles. 



Diameter, without aculei, about 50 p. 



