TERTIARY CALCAREOUS ALGjE. 17 



in a single individual and also a complete intergrading with the cell 

 characters of Lithoporella melobesioides, L. atlantica, and L. conjuncta, 

 as described by Foslie. Form and size of the vegetative cells and size 

 of the conceptacles are the characters relied upon by Foslie to dis- 

 tinguish his proposed species in this genus. The following comparison 

 will, we think, illustrate the difficulty of maintaining species based on 

 these distinctions; the numbers in parenthesis denote occasional 

 extremes: 



Cell dimensions of species, ace. to Foslie: 



L. melobesioides 1903, 30-60 n X 25 /x. 



L. melobesioides 1904, 30-60 (75) ft X (12) 15-25 (30) M . 



L. melobesioides f . varians 1908, 40-54 n X (18) 25-43 xt- 



L. melobesioides f. typica 1909, (25) 30-60 (75) /x X 15-30 (40) n. 



L. melobesioides f. varians 1909, (30) 40-60 (85) ax X (18) 25-43 (54) /x. 



L. atlantica 1906, (32) 36-55 (60) ft X 18-36 (40) fi. 



L. conjuncta 1907, (25) 36-54 (65) xx X 14-29 xx. 



Leeward Islands fossils (19) 23-57 ft X 13-39 /x. 



Conceptacles of species ace. to Foslie: 



L. melobesioides 1903, 600-1000 xx. 



L. melobesioides 1904, 800-1000 xx. 



L. atlantica 1906, 500-800 xx. 



L. conjuncta 1907, (400) 500-800 xx. 



From the above showing it would appear that, unless future researches 

 should reveal conceptacles of a distinctive character, there is little or 

 no ground for considering the Leeward Islands fossil specifically 

 different from recent forms already described. 



Lithoporella melobesioides was originally described as a living species 

 from the Maldives, but has since been reported also as a fossil from 

 New Guinea. 1 L. atlantica and L. conjuncta, both recent species, were 

 described from St. Jan in the Danish West Indies and the west coast of 

 Africa, respectively. All of these were originally proposed under the 

 generic name Mastophora, but in the typical species of Mastophora 

 the thallus consists of several layers of thick-walled cells, which are 

 very slightly or not at all calcined. FoshVs final establishment 2 of a 

 genus Lithoporella to receive the monostromatic calcified forms that 

 he had previously referred to Mastophora seems justified, though 

 Madame Lemoine, in a recent paper, 3 prefers to consider Lithoporella 

 a subgenus of Melobesia. 



Lithoporella pacifica (Heydrich) Foslie, 4 first described as a recent 

 plant of the Hawaiian Islands, is said by Foslie to have cells that are 

 32 to 80 (110) fx by 7 to 12 n, which would make them considerably 

 longer and narrower than those of any of the forms referred to above. 

 Moreover, there are discrepancies of some importance between the 

 descriptions of this plant as given by Heydrich and as given by Foslie, 



1 Siboga Exped. Monog. 61, 1904, p. 75-77, fig. 32. 

 J Kgl. Norske Vidensk. Selsk. Skr. 1909, No. 2, p. 58. 

 B In B0rgesen, Dansk Bot. Ark., vol. 3, 1917, No. 1, p. 174. 



4 Melobesia pacifica Heydrich, Bot. Jahrb. vol. 28, 1901, p. 529; Mastophora (Lithoporella) pacifica 

 Foslie, Kgl. Norske Vidensk. Selsk. 1909, No. 2, p. 53; Lithoporella pacifica Foslie, loc. cit., 59. 



