44 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



Ghaetangiaceae 



Key to the Mexican Genera and Species 



1. Thalli calcareous Galaxaura 5 



1. Thalli non-calcareous 2 



2. Epidermal layer consisting entirely of large, thin walled 



utricles Scinaia 3 



2. Epidermal layer consisting of large, thin-walled utricles 

 (rarely lacking) and numerous 2-3-celled filaments between 



them Gloiophloea confusa 



3. Thalli cylindrical 4 



3. Thalli complanate S. latifrons 



4. Thalli 6-13 cm. high, 3.5-5.0 mm. in diameter 



S. johnstoniae 



4. Thalli 2-4 cm. high, 1.5-2.5 mm. in diameter . S. minima 



5. Thallus distinctly flattened 6 



5. Thallus cylindrical or terete 7 



6. Reproduction asexual G. arborea 



6. Reproduction sexual G. veprecula 



7. Thalli glabrous G. fastigiata 



7. Thalli provided with abundant, extended assimilating filaments, 



at least in lower parts 8 



8. Reproduction asexual 9 



8. Reproduction sexual G. squalida 



9. Tumid basal cells of assimilating filaments absent 



G. filamentosa 



9. Tumid basal cells of assimilating filaments present and prom- 

 inent G. subfruticulosa 



Scinaia johnstoniae Setchell 

 Plate 3, fig. 12; Plate 21, fig. 1 



Setchell, 1914, p. 97, pi. 11, figs. 14-15; Dawson, 1944, p. 257; 

 Dawson, 1949, p. 237, 243. Scinaia complanata (Collins) Cotton, f., 

 as interpreted by Taylor, 1945, p. 146, at least in part. 



Thalli 6-13 cm. high, attached to a stone, a shell or a nullipore by a 

 small discoid holdfast 1-2 mm. broad, 6-9 times dichotomously branched; 

 branches cylindrical, attenuated downwards from 3.5-5.0 mm. in dia- 

 meter above to 1-2 mm. in diameter in basal parts, unconstricted, bright 

 rose-red and quite turgid when alive; central axis faint to moderately 



