9 l \n: LSTRUM. 139 



end and indistinct <>n the other; the result of their being 

 arranged not on the margin but within it. 



The finest, largest and best developed forms, I found in 

 small pools and ditches, Pennsylvania and New Jersey. 



Var. 6PIN08UM, Wolle. I J lat' XL VI, tig. 7. 



The spine (process) protruding near each lateral margin of 

 the semicell, is the peculiarity of tin- variety. 

 Collected near Minneapolis, Minn. 



St. Pseudosebaldi, Wille. Plate XLVI, figs. 8, ''. 



Cells one-fifth part i in width than length, profoundly 



constricted ; spines of the end of the semicells, bifurcate ; rays 

 oearly straight, granular, apices tricuspidate ; vertical view, 

 triangular, sides concave, furnished in the middle with short 

 bifurcate spines. 



Diameter about 75 y. 



Ponds, Pennsylvania and Nen Jersey. 



St. anatim \i. Cooke and Will-. Plate LI. figs. 1. 2. 



Large, granularly rough, or spinous ; semicells in fronl view 

 oval with end- drawn out into diverging arms, apices trifid. 

 End view triangular, sides slightly concave, with angles pro- 

 duced into straight arms; margins in both views ornate with 

 large, emarginate-bifid, or papilliform verrucae. 



Diameter 6080 u.\ length about one-half the diameter. 



Pond-, Mt. Everett, Ma--. 



This species differs from Sfc. Stimuli, in being more slender, 

 not so turgid, arms more protracted, and more evenly clothed 

 with large verrucae. 



St. \i: i ati m, Nbrd. (Var.) Plate \L\'I, figs. 13, 11. 



In Length and breadth about the same; constriction deep ; 

 sinus acute-angled, much ampliated ; semicells elliptic, gran- 

 ularly rough, granule- arranged in transverse series; base 

 convex, top convex or straight, each end furnished with large 

 diverging twinned aeulei : end view triangular, centre smooth ; 

 arm- short with granule- in transverse series; sides furnished 

 with four or more bicuspidate -pine- : angles with two aeulei, 

 only one of which is clearly visible in exact horizontal position 

 of cell. 



Diameter 30-36 ft., without the aeulei. 



