243 
pels me to unite the three described species into one species of 
somewhat variable character, which has to keep the name Halo¬ 
mitra robustra (Quelch). The three forms cited above, which are 
„species“ 
robusta 
irregularis 
si nit er i 
Theca 
extremely 
perforated 
little perforated 
strongly perforated 
Costae 
subdistinct 
(Quelch, Studer, 
Bedot); in quite 
distinet rows 
(Gardiner); 
all stages between 
distinet and 
indistinet 
(van der Horst). 
not distinet. 
in obvious rows. 
Septa 
very distinetly 
radiating from the 
central calicle to 
the edge of the 
corallum 
(van der Horst). 
not arranged in 
rays 
(van der H orst). 
in radiating rows. 
Calicles 
apparently arranged 
around a central 
calicle 
(Quelch, Studer); 
central calicle 
easily recognizable 
(Bedot, 
van der Horst). 
central calicle 
in adult specimens 
not to be 
distinguished from 
the others. 
central calicle not 
distinguishable; 
few secondary 
calicles, no calicles 
in the marginal 
part. 
* 
Columella 
slightly papillose, 
rudimentary 
(Q u e 1 c h); 
pseudocolumella 
(Bedot); 
columella clearly 
visible 
(Gardiner). 
• 
wanting. 
poorly developed. 
Thickness 
of corallum 
20 mm (Quelch) 
15 mm (B e d 0 t). 
thick, heavy. 
10 mm. 
16 * 
