242 Howe : Phycological studies 



Halimeda scabra is similar to Halimeda Tuna in form and 

 habit and it occurs under the latter name in various herbaria. It 

 can, however, be easily distinguished by the always strongly 

 galeate-cuspidate peripheral utricles, a character which, we be- 

 lieve, has thus far been observed in no other species of the genus. 

 These spines or cusps are so large that they are visible under a 

 good hand lens in a properly lighted profile view across a seg- 

 ment-margin even in a dried specimen. The plant is also more 

 strongly calcified than Halimeda Tuna, and the peripheral utricles 

 are smaller in surface view and separate more readily on being 

 decalcified. However, Halimeda scabra bears a stronger resemb- 

 lance in outward form to the typical Mediterranean Halimeda 

 Tuna than it does to a second South Floridan and West Indian 

 Halimeda of the Tuna alliance, with which it sometimes grows 

 associated. This second Halimeda is larger, always smooth, only 

 slightly calcified, of a bright light green color and lubricous when 

 living and more or less papyraceous on drying. Its segments 

 reach an extreme width, so far as observed, of 35 mm.; and in 

 general, the plant may be said to combine characters of Halimeda 

 Tuna platydisca (Decne.) Barton and H. cuneata Hering, as these 

 two are limited and defined by Mrs. Gepp (Miss Ethel Sarel Bar- 

 ton) in her admirable monograph on " The Genus Halimeda." * 

 The lateral walls of the peripheral utricles are in firm contact for 

 |— I their length, as in H cuneata, but the peripheral utricles 

 measure 45— 120 « in surface view, while those of H cuneata are 

 described by Mrs. Gepp as 25— 40/i; the filaments of the central 

 strand separate readily at the joints as in Halimeda Tuna instead 

 of being coherent as in H. cuneata.\ This plant has been met 

 with only in a sterile condition. It seems rather violent to identify 

 it either with Halimeda Tuna or with H. cuneata, and it is possible 

 that further acquaintance with it will show constant and reliable 

 characters for distinguishing it from both. The Halimeda scabra 

 and the smooth plant of the Tuna-cuncata alliance have been more 

 or less mixed in certain American exsiccatae. Thus, in the no. 4.1 



*Siboga-Expeditie. Monographe LX. 1901. 



•f Mrs. Gepp alludes (/.<% p. 16, 17) to a specimen from Rangiroa brought by 

 Professor Agassiz in the Albal7-oss, which forms a connecting link between H. Tuna 

 and II. cuneata, but this has the peripheral utiicles of H. Tuna and the joint con- 

 nections of //. cuneata. 



