T. Holm — Studies in the Cyperacece. 13 



Ctenacanthus acutus sp. nov. 



Medium sized spines with margins of the exserted portion 

 almost perfectly straight, tapering gradually toward the apex ; 

 base deeply embedded ; posterior angles closely set with a row of 

 small denticles arising perpendicularly. Longitudinal costae 

 numerous, triangular in section, bearing minute tubercles on their 

 summits, and denticulated along the sides; increasing by bifurca- 

 tion. Posterior face with a median longitudinal keel. 



Including the two species described above, the Keokuk lime- 

 stone is known to yield six representatives of Ctenacanthus, 

 and in all ten "genera" of ichthyodorulites. Some of the 

 latter, however, are unsatisfactorily determined. Following is 

 a list of the Ctenacanthus species : 



C. acutus Eastman. C. excavatus St. J. and W. 



C. coxianus St. J. and W. G. keokuk St. J. and W. 

 C. cylindricus Newberry. 0. xiphias (St. J. and W.) 



Museum of Comparative Zoology, 

 Cambridge, Mass. 



.Abt. III. — Studies in the Cyperacew / by Theo. Holm. 

 V. Fuirena squarrosa Michx. and F. scirpoidea Yahl. With 

 19 Figures (pp. 25, 26). 



These two species are natives of the eastern United States, 

 F. squarrosa showing a distribution from Massachusetts as far 

 south as subtropical Florida, while the other species is confined 

 to Georgia and Florida alone. It is a marked characteristic of 

 the genus that a true perianth is developed, in our species 

 represented by six leaves in two alternating whorls, those of 

 the inner being spathulate, while the others are merely bristle- 

 shaped like those of Dulichium, Rhynchospora, etc. ; this, the 

 outer, whorl of the perianth is, however, undeveloped in sev- 

 eral of the foreign species of Fuirena, as well as in F. umbel- 

 lata, upon which Rottboll established the genus, first discovered 

 in Surinam by Holander, who described it as " Scirpus triye- 

 talosP The genus is closely related to Scirpus, with which it, 

 also, shows a great resemblance in regard to the general habit, 

 but is well distinguished by the spathulate shape of the perianth 

 as also by the hairy bracts of the flowers, which are smooth in 

 the species of Scirpus. When compared with each other, our 

 two Fuirena-sipecies show several external characters, by which 

 they are readily distinguished, viz : the reduction of the stem- 

 leaves in F. scirpoidea to sheaths with a minute blade, while 

 F. squarrosa has well-developed leaf-blades. The bracts of 



