152 DESMIDS OF THE UNITED STATES. 



A conspicuous species, large, stout and spinous ; variable in 

 the length of the lateral arms; in some cases short, stumpy; in 

 others more elongated ; the spines are also variously promi- 

 nent ; in exact horizontal position they are often not notice- 

 able ; when somewhat turned they become prominent on one 

 end and indistinct on 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. 



Yar. SPixosu^r. Wolle. Plate LVII. fig. 7. 



The spine (process") protruding near each lateral margin 

 of the semi-cell, is the peculiarity of this variety. 

 Collected near Minneapolis, Minn. 



St. PsEUDOSEBALDi, TVllle. Plate LYII, figs. 8, 9. 



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

 constricted : spines of the end of the seuii-cells bifurcate ; 

 rays nearly straight, granular, apices tricuspidate : vertical 

 view, triangular, sides concave, furnished in the middle with 

 short bifurcate spines. 

 Diameter about 75 yu. 



Ponds, Pennsylvania and New Jersey. 



8t. axatixum. Cooke and Wills. Plate LXII, figs. 1. 2. 



Large, granularly rough, or spinous ; semi-cells in front 

 view oval with ends drawn out into diverging arms, ajDices 

 trifid. End view triangular, sides slightly concave, with 

 angles produced into straight arms ; margins in both views 

 ornate with large, emarginate-bifid, or papilliform verrucae. 

 Diameter 60-80 i-i. ; length about one-half the diameter. 

 Ponds, Mt. Everett, Mass. 



This species differs from St. S<J/aldi, in being more slender, 

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

 with large verrucae. 



St. aecuvtum. Xord. (Yar.) Plate LYII, figs. 13, 14. 



In length and breadth about the same ; constriction deep ; 

 sinus acute angled, much anipliated ; semi-cclls elliptic, 

 granularly rough, grannies arranged in transverse series ; 

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

 large diverging twinned aeulei : end view jriangular, center 

 smooth ; arms short with granules in transverse series : sides 

 furnished with four or more bicuspidate .spines; angles with 

 two aeulei. only one of which is clearly visible in exact 

 horizontal position of cell. 



Diameter 30-3(1 /"., without the aeulei. 



