NO. 10 DAWSON: MARINE ALGAE, GULF OF CALIFORNIA 269 



Lithophyllum lithophylloides Heydr. 

 Plate 55, Fig. 3; Plate 58, Figs. 2, 3, 7; Plate 59, Figs. 9, 10; Plate 61, Fig. 1 



Heydrich, 1901, p. 531, with formae bracchiata and phylloides. Lithophyl- 

 lum hracchiatum Lemoine, 1929, p. 44. Lithothamnion racemus 

 Hariot (in part) 1895, p. 169, not of Lamarck. 



Specimens of Diguet's type collection, which has received the particu- 

 lar attention of Heydrich and Lemoine, have been re-examined in the 

 light of recent collections. Some of the author's material has proved iden- 

 tical with Heydrich's form phylloides, and some approaches closely the 

 slender branching form bracchiata. In comparing all these specimens their 

 similarities are far more striking than their differences, particularly the 

 internal structure. It seems best, therefore, to consider them under the 

 same name and to illustrate here some of the degrees of variation in these 

 plants. The size of protuberances is particularly variable as are the 

 amount and form of branching. 



Tetrasporic conceptacles range between 250 and 300 /* and correspond 

 in all material observed. 



The principal internal characters of the plants are the very small size 

 of the thallus cells (7-12 /x in greatest diameter) and their habit of over- 

 growth forming successive layers of tissue through which the prominent 

 and abundant conceptacles may be found at all levels. 



D. 250, 251, dredge-haul in 21 fathoms, west side of Puerto Refugio, 

 shell bottom, Jan. (some specimens identical with type of L. lithophyl- 

 loides f. phylloides) ; D. 572a, bottom of shallow lagoon, San Gabriel 

 Bay; D. 278, 279, dredged in Mejia channel, 12-22 m., Puerto Refugio, 

 Jan.; D. 513, dredged in 16-24 m., sand bottom, Puerto Escondido, Feb. 



Differences in general aspect are often due to the difference in age of 

 surface tissues. Rapidly growing, spreading crusts are composed only of 

 hypothallic tissue of rectangular, closely joined cells. This is brighter pink 

 in color and smoother in texture. When perithallic tissue is developed, the 

 surface becomes more roughened and raised into excrescences. The cells 

 are rounded and in looser "filamentous" vertical rows. In some cases 

 where spreading crusts are growing over old perithallic layers it seems as 

 if two species are present. Conceptacles may be borne in either young or 

 older crusts and are developed successively as the crusts thicken. 



Lithophyllum Digueti (Hariot) Heydr. 

 Plate 59, Figs. 8, 11-16 



Heydrich, 1901, p. 532. Lithothamnion Digueti Hariot, 1895, p. 168. 

 Lithothamnion dentatum Foslie, 1895, p. 4, fig. 15 (not of 

 Hauck.). Lithophyllum Diguetii, Foslie, 1909, p. 26; 1929, pl. 

 LXI, fig. 8; Lemoine, 1911, p. 120. 



