254 MESSES. W. WEST AND G. S. WEST ON 



semicell was deformed and also had one incipient spine at one side ; this certainly belonged 

 to the same species as the one bearing two spines on each side. 



Long. 35 ^ ; lat. s. spin. 32 ^, c. spin. 47 /x ; lat. isthm. 10 /^. 



Xanthidium qiiadricormitum, Eoy et Biss. (in Ann. Scot. Nat. Hist. (1893) p. 245, pi. 4. 

 fig. 5), seems to us very near this species. 



Genus Akthrodesmtjs, Ehrenb. 



97. A. CONVEEGENS, Ehrenb. Infus. p. 152, 1. 10. fig. 18 ; Ralfs, Brit. Desm. p. 118, t. 20. 



fig. 3. 

 One zygospore (diam. 39 ^) of this species was seen from Scarbro', Maine. (PI. XV. 

 fig. 3.) Tbe spines of the species are always incurved as well as convergent, and not so 

 straight as Wolle figures them. 



Var. INCEASSATTJS, Gutw. in Sprawozd. Akad. Krak. xxvii. ii. (1892) p. 64, t. 3. fig. 5. 

 (PL XVI. fig. 4.) 



Long. 33 ^ ; lat. s. spin. 31"5 ^, c. spin. 51 ^ ; lat. isthm. 7'5 ^ ; crass. 17 /x. 



The form seen has the incrassations much more marked. They consist of two trans- 

 verse bars within each semicell near the apex, and are best seen in lateral view as two 

 thickenings. 



Var. OBESUM, nov. var. (PL XVI. fig. 5.) Var. semicellalis a fronte et a vertice visis 



late ellipticis, spinis longioribus. 

 Long. 44-5 /A ; lat. s. spin. 32'5 //,, c. spin. 63 ^ ; lat. isthm. 9'5 ^ ; crass. 24 ^. 



98. A. suBULATus, Kuetz. Spec. Algar. p. 176. 



Long. 46 /x ; lat. s. spin. 38*5 ^, c. spin. 98 />c, ; lat. isthm. 10 /x. 



One form of this is worth mentioning as being similar to that figured by WoUe (Desm. 

 U.S. pi. xxiv. fig. 11), with a higher back, and longer, straighter spines, than the typical 

 form. 



99. A. CURVATTJS, W. B. Turn. Freshw. Alg. of E. India, p. 135, t. 11. fig. 33, t. 12. 



figs. % 8. 

 Long. 50 /x; lat. s. spin. 51^, c. spin. 100^; lat. isthm. 13-5//. 



Genus Staurastrum, Meyen ; Ralfs. 



100. S. APicuLATUM, Ereb. Liste Desm. p. 142, t. 1. fig. 23 ; Cooke, Brit Desm. p. 139. 

 Zygosporae globosse, aculeis longis tenuibus rectis numerosis obsesste. 



Diam. zygosp. s. spin. 23 ^, c. spin. 35 ^. (PL XVI. fig. 6.) 



The zygospores we observed of this species had numerous rather fine and very sharp 

 spines, in all respects very similar to those described for the zygospores of *S'. dejectimh 

 Br^b., and not to those described for S. apiculatum. There is much in this species 

 common with S. dejectum., and as their zygospores so much resemble one another, the 

 two are hardly separable as distinct species, and Lundell (Desm. Suec. i)p. 59-60) was 

 probably correct in placing *S'. apiculatum as a variety of S, dejectum. 



