EHODOMELACEAE. 565 



Family 11. RHODOMELACEAE. 



1. LAURKNCIA Lamour. Essai 42. 1813. 



OSMUNDEA Stackh. Mem. Soc. Imp. Nat. Moscou 2: 56, 79. 1809. 

 Not OSMUNDA L. Sp. PI. 1063. 1753. 



Branching chiefly monopodial. 



Walls of medullary cells of main axes with numerous refringent often lenticular 

 or reniform thickenings,* visible through the cortex; fronds or peripheral 

 branches mostly narrowly virgate, with numerous small 



ultimate ramuli 0.2-0.45 mm. in maximum width. l. L. microcladia. 



Walls of medullary cells of main axes without thickenings ; 



ultimate ramuli mostly more than 0.45 mm. broad. 

 Surface cells of main axes mostly 40-130 w long in sur- 

 face view. 

 Surface smooth or nearly so. 



Plants rather soft and flaccid, usually pink, yellow- 

 ish pink, or green with pink tips ; ultimate 

 ramuli obovoid to subclavate-cylindric. 

 Plants erect, paniculate-decompound, with well- 

 defined leading axes. 2. L. obtusa. 

 Plants decumbent or intertangled, without well- 

 defined leading axes, firmer than No. 2 and 

 with more cylindric ultimate ramuli. 3. L. intricata. 

 Plants rather rigid, purple or greenish purple ; ulti- 

 mate ramuli mostly peg-shaped or verrucaeform. 4. L. Poitci. 

 Surface cells, in apical parts at least, with mammilli- 

 form, conic-rnarnniillate or aculeate papillae. 5. L. ycmmifcra. 

 Surface cells of main axes mostly 20-40 long in surface 

 view ; plants rigid, green or dark greenish purple, cor- 

 neous when dry. 6. L. papillosa. 

 Branching chiefly dichotomous, subdichotomous, or corymbose. 

 Main segments of thallus 0.75-1.2 mm. in diameter ; plants 



mostly 4-12 cm. high ; branches free. 7. L. CoraUopsis. 



Main segments of thallus 0.22-0.45 mm. in diameter ; plants 

 mostly 12 cm. high ; branches more or less concrescent or 

 coherent. 8. L. nana. 



1. Laurencia microcladia Kiitz. Tab. Phyc. 15: 22. pi. 60. f. b, c. 1865. 



Laurencia glomerata Suhr ; J. Ag. Sp. Alg. 2: 753. 1852. Not L. glomerata 



Kiitz. Sp. Alg. 857. 1849. 

 Laurencia obtusa gelatinosa Collins & Hervey, Proc. Am. Acad. 53: 119. 



1917. Not L. obtusa gelatinosa J. Ag. 



Distinguished from all conditions of L. obtusa by its virgate habit, its 

 small ultimate ramuli, and its numerous refringent thickenings of the walls 

 of the medullary cells. 



On rocks and on other algae, low littoral down to 1 m. or more, New Providence, 

 Berry Islands, Great Bahama, Watling's Island, Mariguana, and Great Ragged Island : 

 Bermuda ; and northern South America. Type from the West Indies. 



2. Laurencia obtusa (Huds.) Lamour. Essai 42. 1813. 



Fucus obtusus Huds. Fl. Angl. 586. 1778. 



Laurencia multiflora Kiitz. Tab. Phye. 15: 21. pi. 5S. f. a, b. 1865. 



Very common on rocks and on other algae, at low-water mark and in shallow 

 water, New Providence, Rose Island, Berry Islands, Great Bahama, North Cat Cay, 

 Exuma Chain, Cat Island, Watling's Island, Atwood Cay, Mariguana, Caicos Islands, 

 Great Ragged Island, and Orange Cay : Bermuda ; Florida ; and the West Indies 

 generally ; widely distributed in the warmer seas. Type from southern England. 

 Specimens from Nassau have been reported under name of Laurencia paniculiita by 

 F. S. Collins, Mem. Torrey Club 12 : 14. 1902. 



* The thickenings often lose their refringent character in fluid-preserved material. 



