112 M. FOSLIE. [1905 



Subgen. Eulithophyllum Fosl. 



Rev. Syst. Surv. Melob. (19C0), p. 17; De Toni 1. c. 



1. Lithophylhim oroiculatum Fosl. 



Rev. Syst. Surv. Melob. (1900), p. 19; Lithothamnion orbiculatum Fosl. Norw. 

 Lithoth. (1895), p. 143, t. 22, fig. 10—11; Batt. Cat. Brit. Mar. Alg. (1902), p. 97! 

 De Toni, Syll. Alg. IV (1905), p. 1786. 



Syn : Lithophyllum incrustans f. orbiculata Fosi. in Setch. and Gardn. Alg. 

 North w. Amer. (1903), p. 358 (?). 



This species forms small orbicular crusts at a young stage 

 or often even at a stage advanced, finally, however, becoming 

 more or less confluent. It is firmly attached to the substratum, 

 and attains a thickness of about 1,5 mm., but usually less. It is 

 in fact crustaceous. Sometimes, however, occur excrescences 

 small and irregular, partly even slightly angular, but they seem 

 always to have been formed by covering up and growing over 

 foreign bodies. 



In a vertical section of a crust the hypothallic layer mainly 

 resembles that of Lithoth. Iceve. It is rather feebly developed, and 

 the convergence of the lower anticlines towards the substratum is 

 feeble or wanting. The cells of this layer are of a length twice 

 to four times the breadth, being 12 — 25 p long and 5 — 8 p broad. 

 The perithallic layer is composed of squarish cells 6 — 9 p in dia- 

 meter, or, more frequently, a little vertically elongated, 9 — 14 or 

 up to 18 p long, by 7 — 11 p broad. They are, however, here 

 and there slightly elongated in horizontal direction. Be it said, I 

 have examined but a few sections of small crusts, and in other 

 ones the cells perhaps are larger. 



The conceptacles of sporangia are immersed, at first slightly 

 convex and about 100 — 200 p in diameter, finally slightly decorti- 

 cated, forming shallow, point-like holes, the bottom of which forms 

 a part of the roof, intersected with a single pore. The sporangia 

 are tetrasporic, 100 — 160 p long and 45 — 60 p broad. The con- 

 ceptacles of cystocarps in this species as in many other species 

 appear in other crusts than those of sporangia, but when the crusts 



