2o8 TUFTS COLLEGF STUDIES, VOL. II, No. 3 



7. Segments linear or lanceolate, frond about 6 /j. thick above. 



5. M. pulchrum. 

 7. Segments few, broad ; frond 25-45 M thick ; cells close. 



4. M. arcticum. 

 7. Segments obovate, frond 18-36 /j. thick ; cells not closely set. 



7. M. crepidinum. 



8. Frond not over 30 /a thick, except near the base. 9. 



8. Frond 40-50 /* thick. 12. 



9. Frond not usually much plicate. 10. 



9. Frond usually much plicate. 13. 



10. Cells arranged in distinct groups of 4. 9. M. quaternarium. 



10. Cells not in distinct groups of 4. n. 



ii. Cells in longitudinal and transverse series. 12. M. leptodermum, 



ii. Cells not in series. 8. M. latissiinum. 



12. Chromatophore in cross section not over 9 /j. high. 



6. M. undulatum. 

 12. Chromatophore in cross section about 15 M high. 



10. M. orbiculatuin. 

 13. Frond much lobed, margin distinctly thinner than base. 



10. M. orbiculatuin var. ziariuin. 

 13. Frond not much lobed ; thickness nearly uniform. 



6. M. undulatum var. Farlowii. 



i. M. GROENLANDICUM J. G. Agardh, 1882, p. 107, PI. Ill, 

 figs. 80-83; P. B.-A., No. 13. Frond filiform, tubular, cylin- 

 drical, up to 15 cm. long, from a very slender base expanding 

 to i mm. diameter ; apex broken only at exit of spores. Cells 

 in the lower part of the frond loosely arranged in twos and 

 fours, roundish angular ; in the upper part more evenly distri- 

 buted, more or less closely set. In cross section the membrane 

 is 25-35 /" thick ; the cells radiately elongate, 2-4 times as long 

 as broad ; in the younger parts the central cavity is filled with 

 a gelatinous substance, which disappears as the plant becomes 

 older. Spores or gametes formed first at the summit of the 

 frond, and developing successively in lower cells. Greenland 

 to Mass.; Alaska. 



This plant has no external resemblance to a Monostroma, and 

 was placed in this genus with a mark of doubt by both Farlow 

 and Rosenvinge. It appears like a slender, unbranched Entero- 

 morpha, but seems, however, to be in structure more nearly 

 related to Monostroma. It occurs from April to June in New 

 England ; in July at Newfoundland ; and from May to August 

 in Greenland. On the Atlantic coast it grows in. rather dense 

 tufts, at the lower limit of the literal zone, in company with 



