88 WELWITSCH S AFEICAN FRESHWATER ALG.E, 



11. Xanthidium Ebrenb, (1834), 



1. X. fasciculatum Ebrenb. In/as. 147-8, t. x. f. 24 i (1838) ; 

 Ealfs, Brit. Desni. 114-5. Forma tumore mediano truncato-crenato 

 spinam brevem gereus. Lat. sine spin. 42 // ; lat. cum. spin. 70 /x ; 

 crass, (c. spin.) 46 /i (tab. 368, fig. 16). 



Huilla. In pabidibus exsiccandis ; April 1860. No. 176. 



2. X. cRisTATUM Breb. in Ralfs, Brit. Desm. 115, t. xix. f. 3 

 (1848). 



Var. TROPicuM, var. n. (tab. 368, fig. 15). Var. siuu leviter 

 aperto et acutangulo ; semicellulis subsemicircularibus et leviter 

 angularibus ; spinis brevioribus, paribus apicalibus duabns quam 

 in forma typica, spinis duabus ad angulos laterales, una supra 

 alteram (superiori suberecta, inferior! horizontali), et cum spina una 

 utrobique inter eas ; membrana minute puuctulata, scrobiculis 

 centralibus nullis. Long, sine spin. 38-42 jx, cum spin. 50-52 /x ; 

 lat. sine spin. 33-36-5 ju, cum. spin. 38-44 /x ; lat. isthm. 12-5 jj.\ 

 crass. 19 fj,. 



Huilla. In uliginosis editioribus prope Humpata, Empalanca 

 et Lopollo ; May 1860. No. 15. 



In tbis variety tbere are two more spines on eacb semicell tban 

 in typical specimens of A', cristatwn, and tbe semicells are of a 

 somcAvbat different form; it may perhaps be another species. 



3. X. subtrilobum, sp. n. (tab. 368, fig. 14). X. mediocre, 

 paullo longius quam latius (sine spin.), profunde constrictum, sinu 

 angusto-lineari ; semicellulae distincte trilobfe, lobis quadrangulari- 

 bus ; lobo polari latissimo, apice leviter concavo, angulo unoquoque 

 spina valida erecta et leviter incurvata instructo ; lobis lateralibus 

 spina valida divergenti ad angulos superiores, angulis inferioribus 

 leviter incrassatis, spina minori horizontali acuta (long. 7 fj) in 

 medio marginis lateralis uniuscujusque ; in centro cum annulo 

 granulorum quadratorum 10 circum granulum majus central! ; a 

 vertice visfe anguste oblongae spina acuta ad polos rotundatos, 

 spina utrobique ejus intra marginem, umbone magno granulato ad 

 apicem in medio utrobique, lobo polari rectangular! cum spina 

 valida ad angulum unumquemque ; membrana punctata. Long, 

 sine spin. 50 /x, cum. spin. 69 fx; lat. sine spin. 45 /x, cum spin. 

 60 jtx ; lat. isthm. 17 /x ; crass. 26 /x. 



Pungo Andongo. In stagnis prope Anbilla (Condo) ; March 

 1857. No. 177. 



It differs from X. trilohum Nordst. (in Vidensh. Medd. Naturli. 

 Foren. 1869, no. 14-15, 230-1, t. iii. f. 35 (1870j ) in being more 

 distinctly trilobed with a rectangular sinus between the terminal 

 and lateral lobes, in the lobes being more rectangular, in the 

 presence of a spine in the middle of the outer margin of each 

 lateral lobe, in tbe absence of crenulation at the inferior angles of 

 the latter, in the rectangular polar lobe having but one spine at 

 each angle (as seen in vertical view), and in the narrower vertical 

 view with a more prominent central protuberance. 



Tbis species is close"ly allied to A', (aharatu-acideatum {HuJo- 



