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



A species not closely related to any of the foregoing ; exter- 

 nally characterized by the mostly spherical or broadly pyriform 

 segments. It appears to be a plant of deeper water than most 

 species of the genus. 



5. H. TUNA (Ell. and Sol.) Lamouroux, 1812, p. 186 ; ? Har- 

 vey, 1858. p. 25, PI. XL. A; P. E.-A., No. 1484. Plants not 

 usually over 10 cm. long, moderately calcified, branching in 

 one plane ; a few of the lower segments thick, the others thin, 

 about i mm., varying in form but mostly cuneate, not ribbed, 

 margin entire. Filaments of central strand fused in twos or 

 threes at the apex of each segment ; peripheral utricles 30-70 p 

 cliam., adherent for one-twenty-fifth to one-tenth of their length, 

 rather easily separable ; utricles of subcortical layer 35-no/u, 

 diam.; sporangia globose to pyriform, 200-330 /u. diam., deep 

 green, borne on simple or forked pedicels, on margin or surface 

 of the segments. Fla., W. I. Europe, Asia. 



The group including H. Tuna, H. discoidca and H. seabra is 

 generally distributed in all warm waters, and distinguished by 

 thin, not heavily calcified segments. The roughened surface 

 distinguishes H. sea bra, the slight calcification //. disco/dca . 



6. H. DISCOIDEA Decaisne, 1842, p. 102 ; Howe, 1907, p. 

 .(95, PI. XXVI; P. B.-A., No. 1483. Plants reaching 15 cm. 

 in length and width, very slightly calcified, color bright green, 

 fading when dry ; branched in one plane ; segments deltoid to 

 elliptical with long axis transverse, up to 35 mm. broad, thin, 

 smooth, shining. Filaments of central strand fused in twos, 

 rarely threes, at the nodes ; peripheral utricles 40-85 /a diam., 

 often fusing, in contact with each other for one-fifth to two- 

 thirds their length, not easily separated. Utricles of subcortical 

 layer relatively large, bullate, 110-215 P- diam. Fla., W. I. 



Asia, . l/iica. 



Resembling H. Tuna, but less calcified and of thinner texture ; 

 the segments vary much in size, the largest are broader than 

 long, and of greater dimensions than in H. Tuna ; in cases where 

 the habit is not distinctive the shape and dimensions of the 

 utricles may be depended on to decide. 



7. H. OPUNTIA (L.) Lamouroux, 1812, p. 186; Harvey, 

 [858, p. 23, PI. XL.B; Vickers, 1908, p. 25, PI. XXXV; P. 

 B.-A., No. 123. Plants usually 10 cm. high, sometimes up to 

 25 cm.; more or less branched in various directions; segments 

 much calcified, very variable in shape ; discoid, cordate or tri- 

 lobed ; more or less plainly ribbed ; up to 12X20 mm. Fila- 



