Cushman: Desmids from New England 613 



XANTHIDIUM Ehrenb. 1834 



.49. Xanthidium armatum (Breb.) Rabenh. 



Length without spines 148//; breadth without spines 93//, 

 with spines 115//; isthmus 45 fi. Fairly common, Rose au Rue. 



This species was also common in the material from St. 

 Anthony, but was very much smaller than in that from Rose au 

 Rue. The spines were for the most part simple, those with bifur- 

 cate spines being the exception. A considerable variation was 

 noticed in the specimens from Rose au Rue. An average speci- 

 men from St. Anthony measures: length without spines 96//; 

 breadth without spines 67 u : with spines So a : isthmus X2 u. 



50. Xanthidium antilopaeum (Breb.) Kiitz. 



Length with spines 96 fi ; without 58 fit ; breadth with spines 

 80 fi, without 46 ji ; isthmus 15 fi. 'Occasional, St. Anthony. 



Xanthidium antilopaeum minneapoliense Wolle. 



Length with spines 87 ft, without 68 fi ; breadth with spines 

 75MJ without 53//. Occasional, St. Anthony. 



The specimens of this variety had the lateral spines below the 

 chain of granules. The cells in the variety were larger than in 

 the preceding but the lateral spines were very much shorter. 



51. Xanthidium cristatum Breb. 



Length with spines 72 ft; breadth with spines 56//, without 



spines 40//; isthmus 12 fi. Common, St. Anthony. 



ARTHRODESMUS Ehrenb. 1838 



52. Arthrodesmus convergens Ehrenb. 



Length with spines 45 //, without 32//, breadth with spines 

 45 fi, without 28 fi ; isthmus 6.5 fi. Common, St. Anthony. 



53. Arthrodesmus quadridens Wood. 



Length 34 fi ; breadth with spines 50 fi, without 34 fi; isthmus 



9 ft. Common, St Anthony. 



54. Arthrodesmus Incus Ralfsii W. & G. S. West. 



Length 24 // ; breadth with spines 40 ft, without 19 ft ; isthmus 

 7 fi. Common, St. Anthony. 



