FRESHWATER ALO.E. 49 



TABELLARIACKK. 



Genus DENTICTLA Kiitz. 



70. DENTICULA TExns. 



Var. ANTARCTICA var. nov. 



(PI. TIL, figs. 156, 157.) 



Dentirula fauns Kiitz., Bacill. (1*11). ]>. ):',, t. 17, fig. vnt. ; Smith, Brit. Diatom., ii. (1 *."(), p. L'U. 

 PL XXXIV., fig. 2!):l. 



D. parva valvis late cllipticis apicilms rotuudatis ; costis trausversis validis, 

 0-7 in 10 /A, in media parte rectis, sed polos versus gradatim plus rainusve curvatis ; 

 inter binas costas sunt duse series ptmctarum subtilium, circa 0-7 in quaque serie in 

 media parte valvarum ; polos versus punctae in quaque serie fiunt minus crebrse. 



Long. valv. = 18-23//,; lat. valv. = 7-8 p.. 



Hub. Pond some distance behind hut, Cape Adare, January 9th, 1902; on ice, 

 four feet above frozen watercourse through " Penknife ice," McMurdo Bay, September 

 13th. 1902. 



This was a relatively rare form, of which not many specimens were seen.* The 

 new variety resembles var. frii/iiln ({run. (= D. fri</!<l<i Kiitz.) in some respects, 

 but in the latter the number of costso is not as great as in var. ant < tret !<<<, the costtu 

 are not curved near the poles of the valves, and there are more than two rows of 

 dots between each pair of ribs. There is also resemblance to var. inj/atn (.-Jrun. 

 (= D. iitjlufu W. Smith), in which Smith ("]>. tit,, PL XXXIV., fig. 294) figures 

 many of the costae as curved (</., however, Van Ileurck, Synopsis Diat. Belg. (1880-85), 

 PI. XLIX., figs. 32, 33), but the curvature is different, as the convex surface fa< - 

 towards the poles, whereas in var. tniftirctim it is the concave surface. 



In some of the valves the <-<>st;e near the two ends were curved more towards one 

 side than the other (fig. 150), leading to a certain degree of asymmetry. 



* The form hero described bears an appreciable resemblance to the figure olFragilarin /in/m-i-tirn Castracane, 

 given by Castracane (' Chall.' Rep., Diat. (1886), PL XXV., fig. 12); this figure shows the same characteristic 

 paired rows of clots between each two ribs, and the general shape of the valve is also the same. The ribs are, 

 however, much more delicate and are scarcely curved at the ends of the valves. Van Heurck's figure (nj>. dt., 

 1909, 1'l. III., fig. 48) shows nothing of the punctulations. Sonif dnnbt may bo Ml :v. to whrther the valve figured 

 b\ Castracane roall\ belongs to the genus Pi'niiilnrlii. 



