COSMAKIOL ]21 



constricted, sinus widely open, either a little more or 

 less than a right angle, with a slightly rounded apex ; 

 semicells cuneate, apex truncate and almost straight, 

 superior angles rounded, sides slightly convex. Side 

 view of semicell subcircular. Vertical view elliptic, 

 poles obtusely conical, ratio of axes about 1 : 1'S. Cell- 

 wall smooth. Chloroplasts axile, one in each semicell, 

 with a central pyrenoid. 



Zygospore unknown. 



Length 22-24 //, ; breadth 19-24^; breadth of 

 isthmus 11'5-12/x; thickness 12 //,. 



WALES.- -Plankton of Llyn Cwlyd, Carnarvonshire ! 



IBELAXD.- -Plankton of Lough Corrib, Gralway ! 



This species approaches very closely to C. bicuneatum (Gay) 

 Nordst., but it is much larger, the angles of the semicells are 

 more rounded, and the thickness is much greater. It differs 

 from C. arctoum var. tatricum Racib. in its larger size, its 

 deeper constriction, and in the rounded angles of the semicells. 

 (Consult the remarks on p. 43.) 



It should also be compared with C. subaversum Borge and 

 C. subarctoum (Lagerh.) Racib. 



130. Cosmarium quadratulum (Gay) De Toni. 

 (PL LXXII, fig. 33; PI. XCIII, fig. 4.) 



Euastrum (Cosmarium} quadratulum Gay, Monogr. loc. Conj. 1884, p. 58, 



t. 1, f. 15. 

 Cosmarium quadratulum (Gray) De Toni, Syll. Alg. 1889, p. 934 ; Nordst. 



Index Desm. 1896, p. 216. 

 Ursinella quadratula Kuntze, Eevis. gen. plant. 1891, p. 925. 



Cells very small, a little longer than broad, deeply 

 constricted, sinus narrowly linear with a slightly 



J O i 



dilated apex ; semicells transversely snbrectangular, 

 sides and apex slightly retnse, basal and upper angles 

 obliquely truncate. Side view of semicell elliptic- 

 circular. Vertical view elliptic, ratio of axes about 

 1 : 2. Cell-wall smooth. Chloroplasts axile, one in 

 each semicell, with a central pyrenoid. 



Zygospore unknown. 



Length 12-5-15 /x; breadth 11-12'7; breadth of 

 isthmus 2-3'4/i ; thickness 5'7-6'5 /*. 



