m. 
231 TUN 
elliptice utrinque tuberculo granulato mediano, utroque polo trun- 
cate angulis aculeatis; membrana fuscescens, punctata. 
Long. 0,0032" — 81 gu. Lat. 0,003" — 77 QU. — Crass. 
0,00165" — 42 p. , 
3. X. regulare n. sp. 
X. mediocre, tertia parte circa longius quam latius, non 
profunde constrictum sinu amplo; semicellula ovato-hexagona, 
angulis superioribus et lateralibus in aculeum basi utrinque dente 
parvo preditum productis, a vertice visae ovato-tetragona, angulis 
late truncatis utrinque in aculeum basi utrinque dente parvo pre- 
ditum produclis, in medio aculeis quaternis cruciatim dispositis 
ornata. 
Xanthidiwm. regulare, 190/,. 
& — semicellula e fronte visa. 5 — e vertice. 
Long. s. acul. 0,0026" — 66 u, c. acul. 0,0019" — 48 y. 
Lat. s. acul. 0,0038" — 96 pg, c. acul. 0,0032" — 81 p. 
Constr. 0,0012" — 30 y. 
Ad genus Staurastrum valde accedens. 
Arthrodesmus Ehrbg. 
Inf. p. 449, mut. char.; Archer in Pritch. Inf. p. 736. 
1. A. Incus (Bréb.) Hass. Brit. Alg. p. 357, t. 85, f. 10; 
Ralfs Br. Desm. t. XX, f. 4 b, d; Cosmarium Incus Bréb. in 
Menegh. Syn. p. 228. : 
Interdum in massa quadam gelatinosa involutus. 
Long. s. sp. 0,001—12^ — 285—830 p, c. sp. 0,0024—29" 
— 62—'77 u. Lat. — Long. 
