STAURASTHUM. 135 



author of the name adds, "semi-cells in vertical view trian- 

 gular, sides lightly retuse, angles unarmed." 

 Diameter 60 fi. 



Northampton County, Pennsylvania ; Florida. 



St. Dickiei, Ealfs. Plate LI, figs. 5, 6, 20, 21. 



Semi-cell smooth, subelliptic, turgid ; spines short, curved 

 towards those of the other semi-cell; end view triangular, 

 sides sinuate, angles mucronate. 



Diameter 36-44 ia. 



Cells are about as long as broad ; semi-cells elliptic, but 

 having the outer margin more convex than the inner one ; 

 the mucros or spines, short, curved, and directed inwardly. 

 It occurs not infrequently in Pennsylvania, New Jersey, 

 Massachusetts, and probably in every State. 



St. aeistifeeum, Ealfs. Plate LI, figs. 15, 16. 



Semi- cells smooth, triangular, constricted near the angks, 

 producing a mammillate appearance. Each angle furnished 

 with a long awn ; end view with three, or rarely four awned 

 lobes. 



Diameter 15-20 fA.. without the awns or spines, and with 

 them fully twice the size. 



-Rather rare, but it has been found in many States, from 

 Rhode Island, New Jersey, to Georgia. 



St. Lewisii, Wood. Plate LI, figs. 26, 27. 



Smooth, with very ample sinus, obtuse-angled, which is 

 armed with a small spine ; semi-cells from the front broadly 

 triangular; from the vertex, triangular, with the angles 

 somewhat tumid and rounded ; angles furnished with a very 

 large, acute, robust spine. 

 Diameter with the spines, 62 /i. 



This species was first found by Lewis, in Saco Lake, N. H., 

 and since only in one locality, the past Summer, 1883, by Miss 

 Eloise Butler, of Minneapolis, Minn. 



St. cuspidattjm, Breb. Plate LI, figs. 23-25. 



Semi-cells smooth, fusiform, connected by a long narrow 

 band; aculei parallel or converging; end view triangular, 

 or rarely quadrangular, with inflated aculeated lobes. 

 Diameter 25 ja. ; length 30 yw. 



Quiet waters, Pennsylvania and New Jersey, but not 

 frequent. 



