140 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



Type locality: Rocky shore at Punta Colorado, near Guaymas, 

 Sonora, Mexico. 



Additional material: Gulf of Calif. — D. 395-40, Bahia Te- 

 poca, Feb.; D. 460a-40, Isia Esteban, Feb.; D. 1693, Bahia Carrizal, 

 near Guaymas, May; D. 979, Bahia Agua Dulce, Isla Tiburon, Feb.; 

 D. 7139a, Bahia Agua Verde, Mar.; D. 3114, 5 km. north of Cabo 

 Pulmo, Nov.; D. 3179, between Eureka and Riberia, Nov.; D. 3219, 

 Punta Palmilla, Nov. ; D. 3382, Cabeza Ballena, Nov. Jalisco — D. 

 3755, Barra de Navidad, Dec. (juvenile material). 



This species shows in habit, gross morphology and in internal struc- 

 ture considerable resemblance to Amphiroa zonata with which it may 

 often be found growing in the Gulf of California where the ranges of 

 the two plants overlap. Although it may not always be possible to dis- 

 tinguish young plants or terminal fragments of A. subcylindrica from 

 A. zonata^ sufficient distinctive characters of mature, whole plants can 

 be pointed out to make reliable determinations. In the first place, A. 

 subcylindrica is a plant of the southern Gulf of California and probably 

 also of the mainland coast to the south. It does not appear in collections 

 from Pacific Baja California. It is generally coarse and more nearly 

 cylindrical in most parts than A. zonata. It is more heavily calcified and 

 the intergenicular cortex is usually so thick, even in young segments, 

 that the clear, zonal markings found in A. zonata are indistinct or 

 absent. Structurally the most striking differences are to be found in old 

 segments where the repeated secondaiy grovv^th of the cortex makes it 

 very thick and in which repeated crops of conceptacles are arranged tier 

 on tier. The conceptacles, being rather well embedded and their ostioles 

 commonly calcified over, are inconspicuous from the surface. 



The more critical examination of the now ample Gulf of California 

 material shows that this species differs from A/nphiroa rigida, as under- 

 stood both by Weber van Bosse and by B^rgesen, in its usually more 

 robust habit, less fragile nature and in the structure of the genicula. 



Amphiroa drouetii sp. nov. 

 Plate 27, figs. 5-6 



Amphiroa pusilla Yendo, as interpreted by Dawson, 1944, p. 276 in 

 part. 



Thallis fasces compactos, pulvinatos ad 2.5 cm. altos, 5 cm. latos 

 edentibus ; ramificatione dichotoma, plus minusve decussata ; ramis cylin- 

 dricis usque etiam compressis, 350-550 /x diametro, rigidis, plane baud 

 segmentatis; geniculis calcificatione maxime tectis, late separatis; inter- 

 geniculis semel, bis, terve furcatis. 



