398 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



species can be distinguished in the Florida- West India region, 

 and fairly distinct habit characters can usually be found, but 

 doubtful cases requiring decalcification and microscopical exam- 

 ination are not uncommon. 



KEY TO THE SPECIES OE HAMMKDA. 



i. Branching iu more than one plane. 7. H. Opmitia. 



i. Branching in one plane only or with few exceptions. 2. 



2. Peripheral utricles cuspidate. 8. II. scabra. 



2. Peripheral utricles not cuspidate. 3. 



3. All segments except those bearing branches cylindrical. 



2. H. Monilc. 



3. Most segments ovoid or flattened, not cylindrical. 4. 



4. Peripheral utricles over 150 /j. diam. ; dried frond showing pitted 

 surface when slightly magnified. 10. H. favnlosa. 



4. Peripheral utricles not over 80 /x diam. ; surface not pitted. 5. 

 5. Segments distinctly ribbed. i. H. Iridcns. 

 5. Segments indistinctly or not at all ribbed. 6. 



6. Segments slender, cuneate to cylindrical. 3. H, gracilis. 



6. Segments broader, often broader than long. 7. 



7. Very slightly calcified ; color pale. 6. H. discoidea. 



7. More calcified ; color darker. 8. 



5. Segments mostly with crenulate, dentate or lobed margins. 



9. H, siinii/aiis. 



8. Segments mostly with entire margins. 9. 



9. Segments thin, more or less cuueate, moderately calcified. 



5. H. Tuna. 

 9. Segments obovoid. pyrit'orui or globose, heavily calcified. 



4. H. lacriinosa. 



i. H. TRIDENS (Ell. and Sol.) L,amouroux, 1812, p. 186; 

 Harvey, 1858, p. 24, PL XUV.C. ; P. B.-A., No. 1487. Plants 

 up to 20 cm. high, thickly calcified, especially below, branched 

 in one plane, very variable in habit. Segments ribbed, tri- 

 dentate, cuneate or discoid, often welded together near the 

 base ; lower segments cylindrical, up to 8 mm. diam. ; tridentate 

 segments up to 14 mm. wide. Filaments of central strand either 

 communicating with each other at apex of segment by pits, 

 or rarely free throughout; peripheral utricles 49-77 ^ diam., 

 rather loosely attached, in contact for one-eighth to one- 

 twentieth of their length ; sporangia obovoid or pyriform, 200- 

 380/0. diam., color dark yellow or brown, on rather long, several 

 times dichotomous pedicels. Flu., W. I. AH 'carm seas. 



Forma typica (Barton) nov. comb.; //. incrassata forma fjpica 

 liarton, 1901, p. 27. Lower segments cylindrical; upper seg- 

 ments more or less trilobed. 



