FRESHWATER ALGJ3. 41 



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

 loose arrangement of the trichomes, the narrow sheaths, the rather wider trichomes 

 and in the spores. Unfortunately the authors give no details as to shape or size of 

 the heterocysts. 



N. longstaffi, appears more nearly related to N. cuticulare (Breb.) Born, et Flah., 

 but there are striking differences, viz., the non-confluent thalli and the heterocysts, 

 which are nearly double the size of the vegetative cells. 



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

 modified as follows : 



Srtt. i . Plantse aquaticse, maculif ormes, adnatae vel postea libere natantes, ambitu 



crcscentes ; fila laxe vel arete contorta ................................................... CUTICITLARIA. 



(a) Trichomata 8-4 p. crassa, dense contorto-flexuosissiina ; sporje sphaericae. 

 Heterocystse eadem forma et magnitudine nt artieuli vegetativi vel 



paulo crassiores ; sporae sphrcrieae 8-10 //. crassaa .................. N. cuticulare. 



Heterocystte diametro articuli vegetativi ca. duplo latiores ; sporas 



sphajricfe, 5^ crassae ...................................................... N. longstafli, sp. n. 



(V) Trichomata 2 5-4 p. crassa, laxiora ; sporffi sphaericaa vel depresso- 



globosae, in longas catenas seriate. 

 Trichomata 3 5-4 /* crassa ; sporae sphaaricaa ssepius 6 /j. crassaa, in 



longas catenas seriatas ; heterocystas ? ................................. N. maculiforme. 



Trichomata 2 5-3 5 p crassa ; sporae depresso-globosaa vel rarius 

 globosa3, in catenis dispositis ; heterocystaa diametro articuli 

 vegetativi ca. duplo latiores ............................................. N. disciforme, sp. n. 



60. NOSTOC HEDERUL^E. 



Nostoc Hederulce Meneghini ; Bornet et Flah., op. cit., vii. (1888), pp. 189-190 (N. punctiforme (Kiitz.) ; 

 Hariot, Journ. de Bot., v. (1891), p. 29). 



G a p pond, Winter Harbour (on Phormidium). 

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

 more or less spherical cells. 



61. NOSTOC FUSCESCENS sp. n. 

 (PL III., figs. 138-144.) 



Thallo ab initio globoso, primo adnato (?), postea libere natante, flavo-fuscescenti, 

 fusco vel nigro-fuscescenti, setate provecta plus minusve cavo et interdum lacerato, 

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

 trichomatibus laxe intricatis, ssepe valde contortis, interdum parallelis ; vaginis in thallis 

 parvis et in partibus exterioribus thallorum seniorum distinctis, lamellatis, plerumque 

 in duas regiones disjunctis, regione exteriore diffluenti hyalina vel dilute flavo- 

 fuscescenti plus minusve inter cellulas constricta, regione interiore densiore distincte 

 delimitata fusca vel nigro-fuscescenti et inter cellulas valde constricta (ssepe simili 

 septationis), in partibus interioribus thallorum seniorum ssepe dilute flavo- 



M 2 



