WISCONSIN PHYTOPLANKTON 129 



The few individuals that have been seen agree well with W. & G. S. 

 "West's drawings of the alga as it is found in India. More reliance 

 should be put in their figures than on that of Turner which is merely 

 a copy of a sketch by Wallich. The organism belongs in the group 

 of short-spined species and is distinguished by the marked concavity 

 of the apex of the semicell. 



6. Arthrodesmus constrictus G. M. Smith. PI. 85, Figs. 6-8. 

 Trans. Wis. Acad. Sci., Arts & Lett. 20: 348, pi. 10, figs. 17-18. 1922. 



Cells fairly small, breadth (without spines) somewhat greater than 

 the length, deeply constricted, sinus a broad excavation with a sub- 

 rectangular apex and sides opening outwards, isthmus narrow and 

 greatly elongate; semicells broadly obversely triangular to trans- 

 versely elliptic, apex somewhat tumid, lateral angles of semicells acute 

 and each with a single fairly long gradually attenuated spine, spines 

 divergent. Vertical view narrowly elliptic and with a single straight 

 spine at each pole. (Euplanktont.) 



Zygospores unknown. 



Cells 27-35 fi long with spines, 20-25 ju, long without spines ; breadth 

 with spines 52-58 /t, without spines 25-28 ix ; breadth at isthmus 4-5 fi ; 

 spines 15-18 /* long, 



Bass (rrr), Blue Gill (rr), Carson (rrr), Horseshoe (rrr), Jenny (rrr), Lynx 

 (rr), Pine Tree (rrr), Pokegama (rrr). 



Showing a close relationship to both A. incus (De Brebisson) Has- 

 sall and A. triangularis Lagerheim, but differing in the much greater 

 breadth of the semicell in proportion to the length. An elongate 

 isthmus similar to that found in this species is known in certain 

 varieties of A. incus but the narrowness of the isthmus is much more 

 pronounced in A. constrictus. 



7. Arthrodesmus Ralfsii W. "West. PI. 85, Figs. 9-12. 



Jour. Linn. Soc. Bot. 29: 168. 1892. 



Arthrodesmus incus var. Beta Ealfs, Brit. Desm. 118, pi. 20, figs. 4E-4L. 1848. 



Arthrodesmus incus var. Balfsii (W. West) W. & G. S. West, Monogr. Brit. 

 Desm. 4: 95, pi. 114, figs. 2-4. 1912. 



Arthrodesmus incus var. Ralfsii forma latiuscula W. & G. S. West, Monogr. 

 Brit. Desm. 4: 96, pi. 114, fig. 5. 1912; G. M. Smith, Trans. Wis. Aead. Sci., Arts 

 & Lett. 19': 647. 1918. 



Cells small, length about equal to the breadth (without spines), 

 median constriction fairly deep, sinus widely open and with apex 

 semicircular, isthmus broad but not elongated; semicells obversely 

 trapezif orm, with bases straight to slightly convex, apex straight or in 

 rare cases slightly concave ; lateral angles of semicells acute and bear- 

 ing short stout gradually attenuated spines ; spines convergent. "Ver- 

 tical view elliptic, with a single spine at each pole. (Facultative 

 planktont.) 



