5 
New British Freshwater Algae. By William West. 
Genus Cosmarium Corda ; Ralfs. 
C. subretusi forme sp. n. Fig. 20. 
C. miiiutissimum, 1^-plo longius quam latius, sub- 
modice constrictum. sinu aperto et obtuso ; semicellulae sub- 
rectangulares, angulis inferioribus late rotundatis, lateribus 
prope angulos superiores acutos retusis, apicibus latissime 
truncatis (rectis) ; a vertice visae ellipticse polis subacutis ; a 
latere visae subrotundatae ; membrana glabra. 
Long. 7 * 8-8 //, ; lat. 6 * 2-6 '5 /a; lat. apic. 5 * 5 /* ; lat. 
isthm. 4*5 fi ; crass. 3 fi. 
Eab. Borrowdale, Lake District. 
This approaches G. retusiforme (Wille) Gutw. Flora gl. ok. 
Lwowa, 1891, p. 55, tab. ii. fig. 12 [ = C. Hammeri Reinsch var. 
retusiforme Wille (Bidrag til kunds. om Norges Ferskv. Alg., p. 32, 
t. i. f. 16)] in its front view, but differs in its very much smaller size, 
its broader apices, and in its different lateral and vertical views. 
C. Holmiense Lund., Desm. Suec., p. 49, tab. ii. fig. 20. 
var. undatum var. n. Fig. 12. 
Var. minor, semicellulis truncato-pyramidatis, utrobique 
triundulatis ; latitudo apicis dimidium diametri 
basis ; membrana delicatissime punctata. 
Long. 56 /x ; lat. 34 //, ; lat. isthm. 13 /i ; crass. 27 ya. 
Eab. Glen Shee, Perthshire, Scotland. 
C. tetragonum (Nag.) Arch, in Pritch. Infus., p. 732 ; Euastrum 
tetragonum Nag. Einz. Alg., p. 119, t. vii. a, f. 5. 
var. pumilum var. n. Fig. 19. 
Var. minor, semicellulis truncato-pyramidatis, apicibus 
non undulatis. 
Long. 22*5 /*; lat. 12*5 /x ; lat. isthm. 7*5 /^ ; crass. 
7-5 /x. 
Eab. Ben Laoigh, Scotland. 
This is but half the size of the type and the semicells ar&~more 
pyramidate with straight apices. 
C. Lundellii Delp., Spec. Desm. subalp., p. 109, t. 76, f. 62-64. 
var. ellipticum var. n. Fig. 11. 
Var. minor, longior quam latior, cum isthmo angustiore. 
Long. 68 yL6 ; lat. 53 yit; lat. isthm. 16 ^ ; crass. 26 /jl. 
Eab. Ben Laoigh, Scotland. 
Compare with C. galeritum Nordst. (Desm. Bras., t. iii. f. 26) and 
G. corruptum Turn. (Freshw. Alg. of E. India, p. 51, t. viii. f. 2). 
C. pyramidatum Breb. in Ralfs, Brit. Desm., p. 94, tab. xv. fig. 4. 
var. angustatum var. n. Fig. 18. 
Var. angustior, paene duplo longior quam latior, angulis 
inferioribus non rotundatis sed paene submamillatis, 
lateribus rectioribus. 
