ui i, n i flabellules, arranged normally in subverticils around 



the rhachis, and vai inch in size, being io mm or more in length. In R. phoenix the 



rticil are usually laterally connate into collars which mon 01 



lachi rhe rhachis appears to have a power ol contirtuous but 



slow growth in I youngest Flabellules are found at the apex of the rhachis, which 



| n / v ' longer or shorter than the capitulum. When the rhachi is longer, the 



ipitulum is conical, owing to the gradual diminution in size of the successive 



on the < «t li< r hand the rhachis is shorter, i ï 1 « - capitulum terminates in an 



.; the bottom of which are seen the youngest flabellules. This is sometimes the 



in A'. phoenix, but nearly always in A'. oblongus — at least in fresh or pickled plants; 



in dried herbarium specimens the cavity escapes notice, having become closed as the result 



of pressure in dr) ing. 



\\ hai the limit of the apical growth <>f the rhachis is «e do not know. We give, 

 under R. phoenix f. longi/olius, a description of a unique specimen of twice the ordinary 

 rhe total length of the stipes is 15 cm. and the flabellules .w<- nearly 5 cm. long. It is 

 quite easy to explain the existence of such an abnormally large plant ol R. phoenix by means 

 of the theory of continued apical growth, young flabellules being continually added above, 

 while the older om-s drop off below. This continued growth of the rhachis forms one ol the 

 fundamental differencés between this genus and Penicillus. 



The flabellules of RhipocepJialus arise as branches of the main filaments within the 

 stipes. Each such branch passes out through the cortex and soon divides dichotomously, first 

 at quite short, then at greater or vastly increased distances, but always in one and the same 

 plane, diminishing in diameter at each dichotomy. The component filaments are parallel, being 

 either laterally coherent [R. phoenix), or approximated but free 1 A'. oblongus). Their external 

 pellicle is calciticd and porous. 



The geographical distribution of the genus ranges from Florida to Guadeloupe. The 

 plants appear to grow in colonies on coral sand in calm and shallow waters. 



Sy st e m a t i c. 



The two species which compose this genus are easily distinguished from one another, 

 by the composition of the flabellules, the filaments of which are narrow and laterally coherent 

 in R. phoenix, and free from one another and 2 —3 times as thick in R. oblongus. 



The genus itself broadly resembles Penicillus in size and genera! habit, but is distin- 

 guished from it l>y the possession of flabellules in contrast with the fascicles which compose 

 the capitulum of Penicillus. The flabellule of Rhipocephalus is a branch-system with the dicho- 

 tomie, arranged all in one plane and is fundamentally distinct from the fascicle of Penicillus, 

 which has its dichotomies arranged in alternating planes Another point of difference is that 

 in Rhipocephalus the rhachis poss< es the power of continued apical growth, whereas in 

 Penicillui the apical growth is limited. 



tppear to us to be amply sufficiënt to indicate that these two genera, 



