Those of the first cycle alone are large and conspicuous ; they are a little exsert, a little 

 unequal in size, and they descend straight to the very bottom of the cup, where they meet. 

 Corallum snow-white, the pedicle with a faint cinnamon-brown suffusion. 



Greatest height of corallum 1 8 millim. 



Major diameter of calicle 8 „ 



Minor „ ., „ 7 « 



The characteristic feature of the corallum of this species is the burial of the septa of 

 the 3''^^ and 4"^ cycles in the depths of the cup where at first they escape notice. Its nearest 

 relative seems to be D. simplex Verrill (American Journal of Science and Arts, 1870, p. 371) 

 from the West Indies. 



XVIII. Flabellum Lesson, E. & H., Duncan. 



The identification of the species of this genus presents difficulties which, in the absence 

 of actual types for comparison, are insuperable ; for many of the species are not only highly 

 variable, but they also undergo radical changes of form in the course of growth, these changes 

 affecting the shape of the corallum, the form and size of the columella, and the number of the 

 septa. No one can be more dissatisfied than I am myself with the present attempt to determine 

 the large number of forms collected by the "Siboga". 



Synopsis of the Siboga Deep-sea spfeies of Flabellum. 



Corallum free or becoming so: — 



I. Corallum shaped like a fully-open fan : — ■ 



1. Septa in six or more cycles: — 



I. The larger septa form 48 compartments each of which 

 contains 3 smaller septa: the circumference of the 



corallum is less than a semicircle \. F. distinctuin. 



II. The larger septa form 48 compartments each of which 

 contains 7 smaller septa: the circumference of the 

 corallum is much more than a semicircle . . . . 2. F. lamcllulosum. 



2. Septa in 5 cycles, the last cycle incomplete: lip of calicle 



jaCTged 3- -^- laciniatuiii var. 



II. Corallum shaped like a nearly-open fan : septa in 5 complete cycles : 



lip of calicle jagged 4. /". sulncnse. 



III. Corallum either a half-open fan, or a compressed cone : — 



1. Septa in six or more cycles: — 



I. Lateral costa; sharp or jagged 5- ^- australc. 



II. No lateral costa; 6. F. latum. 



2. Septa in five cycles, the fifth cycle incomplete; lateral costai 



sometimes spinose 7- P^- lycgi'larc. 



3. Septa in four cycles: no lateral costs %. F. dens. 



IV. Corallum an open oval cup: septa in five cycles, with the inferior 



cycles incomplete (^. F. japonkuvi. 



