NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 19 



Acrochaetiaceae 



Key to the Mexican Genera and Species'^ 



1. Plants saxicolous .... Rhodochorton purpureum 



1. Plants not saxicolous 2 



2. Chromatophore parietal or laminate . Acrochaetium 3 

 2. Chromatophore stellate Kylinia 15 



3. Plants endozoic 4 



3. Plants endophytic, at least with endophytic basal 



filaments 5 



3. Plants epiphytic, superficial 7 



4. Plants endozoic in ascidians . . A. asctdiophilum 

 4. Plants endozoic in hydroids . . . . A. penetrale 

 4. Plants endozoic in sponges . . . A. spiculiphilum 



5. Free filaments scarcely extending beyond host ; in 



Bonnemaisonia A. bonne?naisoniae 



5. Free filaments long 6 



6. Endophytic in Helminthocladia . . . A. bornetii 

 6. Endophytic in the genicula of articulated 



corallinaceae A. amphiroae 



6. Endophytic in Codium . . . . A. rhizoideum 



7. Plants attached by a single basal cell 8 



7. Plants attached by a multicellular base 11 



8. Thalli less than 300 fx high 9 



8. Thalli more than 300 [x high 10 



9. Primary branches alternately branched, terminating in 



a slender hair A. eastwoodae 



9. Primary branches secundly branched, blunt . A. punctatum 



10. Basal cell unenlarged A. hancockii 



10. Basal cell much enlarged . . . . A. sinicolum 

 11. Thalli minute, mostly under 50 ju, high . . A. scinaiae 



11. Thalli larger, over 500 /x high 12 



12. Branching predominately opposite . . A. plumosum 

 12. Branching predominately secund or alternate ... 13 

 13. Monosporangia borne on adaxial branchlets forming 



axillary clusters A. daviesii 



1 Dr. Jean Feldmann has called my attention to the similarity between Acro- 

 chaetium grateloupiae Dawson (1950, p. 153, figs. 22-23) and Callithamnion 

 endo'vaginum Setch. & Gard. It now appears that I was in error in describing 

 the former as new, and that it should be treated as a synonym of the latter. 



