FRESHWATER ALG.E. 41 



following respects : the very regular oval or circular shape of the thallus, the invariably 

 loose arrangement of the tricbomes, the narrow .sheaths, the rather wider trichomrs 

 and in the spores. Unfortunately the authors give no details as to shape or si/c of 

 the heterocysts. 



\. longstaffi. appears more nearly related to N. cufic/ilun' (Breb.) Born, et Flah., 

 but there are striking differences, viz., the non-confluent thalli and the heteror\ -is. 

 which are nearly double the size of the vegetative cells. 



Boruet and Flahault's key to the species of this section may therefore be slightly 

 modified as follows : 







Si-i'f. 1. Planta; aquatica?, maculiformcs, adnata? vel postea liberc natantes, ambitu 



cruscentes ; fila laxe vel arete contorta CUTKTLAIUA. 



(a) Trichomata 3-4 /j. crassa, dense contorto-flexuosissima ; spone sphsericiL 1 . 

 Heterocystaj eadcm forma et magnitmline nt articuli vegetativi vul 



paulo crassiores ; sponc sphscricse X-l(i ^ crassie X. rntii-nl<tr>'. 



Heterocystaj diametro articuli vegetativi ca. duplo latiores ; sporre 



sphrericae, 5/t crassie .V. hnt/stupi, sp. n. 



(//) Trichomata i' ">-4 p. crassa, laxiora ; sporie sphaerica) vel di-presso- 



glubosa?, in longas catenas seriats. 

 Trichomata 3'5-4/x. crassa; sponc spbwrica 1 sre]iius 0/z crassai, in 



longas catenas seriatre ; lieterocystse ? j\ T . ni,tnilifnnnc. 



Trichomata 2 u-3 5 ft, crassa ; sporaj depresso-globosaa vel rarius 

 globosa?, in catenis dispositis ; beterocystfe diametro articuli 

 vegetativi ca. dnplo latiores N. itiscifonne, sp. n. 



60. NOSTOC HEDERUL.E. 



Nostoi- /fi'i/n-i/lif Menegbini ; Bornet et Flah., o/i. eit., vii. (isss), pp. 189-1 '.li'i (X. pnnc1ifnnp (_Kutz.) ; 

 Ilariot, Journ. de Bot., v. (1891), p. 2!i). 



Hub. Gap pond, Winter Harbour (on Phonniiliuin). 



JMiuutc colonies of very diverse shapes with very densely crowded filaments of 

 more or less spherical cells. 



r>i. NOSTOC FuscEscExs sp. n. 

 (PI. III., figs. 1:38-144.) 



Thallo ab initio globoso, primo adnato(?), postea libcre nataute, rtavo-fuscescnit i. 

 fusco vel nigro-fuscescenti, aetate provecta plus minusve c-avo et iuterdum lacerato, 

 diametro usque ad 10 mm., peridermate tenui levi mucoso facile lacerato circumdato ; 

 trichomatibus laxe iutricatis, srepe valde coutortis, interdum parallelis ; vagiuis in thallis 

 parvis et in partibus exterioribus thalhirum seuiorum distinctis, lamellatia, plerumque 

 in duas regiones disjuuctis, regione exteriorc diffluenti liyalina vel dilute flavo- 

 fuscescenti plus minusve inter cellulas coustricta, regione iuteriore densiore distincte 

 delimitata fusca vel nigro-fuscescenti e.t inter cellulas valde constricta (saspe simill 

 septationis), in partibus interioribus thallorum seniorum ssepc dilute tlavo- 



M - 



