The Plankton Algae of the Palisades Interstate Park 139 



Semicells broadly elliptic, with an arcuate row of pores just below 

 the apex. Lateral margins of semicells with two robust, upwardly 

 curved spines. 



Length 45-48 /x ; breadth without spines 43-47 /a, with spines 65-75 

 /x; length spines 12-15 ix; breadth at isthmus 9-12 /x. . 



This alga suggests very strongly the one which Johnson referred 

 to X. antilopaeum var. javanicum Nordst. The two stout spines at 

 the lateral angles of the semicells show that it belongs to the X. 

 hastiferum-suhhastiferum-controversum group of species that have 

 two pairs of spines on the lateral margins. The cell shape is that of 

 X. subhastiferuni but it differs in the curved spines and the subapical 

 ornamentation. 



Staurastrum trihastiferum sp. nov. PI. 17, Figs. 5-6. 



Cells very large, breadth (without spines) i. 5-1. 75 times the 

 length, deeply constricted, sinus widely open and with an acute apex, 

 isthmus narrow. Semicells obversely semicircular, apices markedly 

 tumid, lateral angles rounded and bearing a single long, stout, solid 

 spine. Spines subparallel and generally slightly outwardly divergent 

 at their apices. Vertical view triangular, sides somewhat retuse in the 

 central portion, angles fairly sharp and bearing a single stout spine. 

 Cell wall coarsely punctate. 



Zygospores unknown. 



Length 90 /x; breadth without spines 77-93 fi, with spines 1 15-138 

 IX] length spines 22.5-30 /x; breadth of isthmus 24 [x. 



This desmid is separated from other species bearing single spines 

 at the corners of the semicells by its large size. It should be com- 

 pared with 5^. minnesotense Wolle and ^. longispinum var. bidentatum 

 (Wittr.) W. & G. S. West, which dififer in having two large spines 

 at the angles of the semicells. 



Staurastrum chaetoceras (Schrod.) comb. nov. PI. 18, Fig. 3. 



Staurastrum polyniorphum var. chaetoceras Schroder in Zacharias, Forsch- 

 ungsbr. a. d. Biol. Stat, zu Plon 6: 131, text figs. a-c. 1898. 



An alga which is worthy of specific rather than varietal rank. 



Staurastrum Johnsonii var. triradiatum var. nov. PI. 18, Figs. 



5-7- 



Vertical view triangular ; ornamentation of the front view as in the 

 biradiate type. 



Length without processes 32-42 ix, with processes 50-64 jx ; breadth 

 with processes 55-75 ix', breadth isthmus 8.5-1 1.5 /x. 



This variety resembles S. cingulum (W. & G. S. West) G. M. 

 Smith, in the general cell shape and transverse row of granules just 

 above the isthmus ; but the ornamentation of the apices of the semi- 

 cells, the verrucae and the subapical rings of minute verrucae, is that 

 of 6*. Johnsonii. 



Staurastrum pseudopelagicum var. minor var. nov. PI. 18, 

 Figs. 13-14. 



Length without processes 16.5-22.5 /x, with processes 30-38 /x: 

 breadth with processes 42-50 [x; breadth isthmus 6-7 fx. 



