The Echinoderm Fauna of South Africa. 379 



ARBACIIDAE. 



The discovery of a representative of this family in South African 

 seas was one of the interesting results of the VALDIVIA'S collecting 

 on the Agulhas Banks. Doderlein, at first, considered it identical 

 with the West Indian representative of the same genus but later 

 decided it was a distinguishable variety. In the PIETER FAURE col- 

 lection is a magnificient specimen of what is apparently the same 

 species, which convinces me that the form may well be recognized 

 as a valid species, under the following name. 



COELOPLEURUS INTERRUPTUS. 



Plate XXI. Fig. 3. 

 Coeloplvurus floridanus Doderlein, 1906. VALDIVIA Ech., p. 181 



A. Agassiz, 1872). 

 Coelopleurus floridanus var. interrupta Doderlein, 1910. Jena. 

 Denkschr., vol. 16, p. 257. 



Doderlein had but a single small example (18 mm. in diameter) 

 of this interesting species and as he had no specimen of floridanus 

 at hand for comparison, it is not strange that he referred it to the 

 West Indian species, and gave no detailed description. The PIETER 

 FAURE specimen is 43 mm. in diameter, somewhat larger than the 

 largest specimen of floridanus in the M. C. Z. collection. On com- 

 paring the two specimens one finds the following differences of taxo- 

 nomic importance. 



In the first place the colouration of the Cape specimen is totally 

 different from that of floridanus. In the latter the bare interambu- 

 lacral area is prevailingly blue-violet, clearest on the distal half of 

 the genital plate and fading out rapidly towards the ambitus; there 

 are small blotches of pale brown proxirnally which increase rapidly 

 in size so that the brown occupies a much larger area than the 

 blue-violet; the sides of the interambulacra are bright scarlet-red, 

 the prevailing tint of the ambulacra. This general pattern of colora- 

 tion is shown in all (16) of the specimens of floridanus in the M. 

 C. Z. collection, the only diversity being in the brightness of the 

 shades and their relative extent; in some young individuals, the 

 brown is wanting and there remains the blue-violet and scarlet in 

 vivid contrast; more commonly the shades are paler or duller and 

 the brown is replaced by greenish-white or dirty whitish ; some dry 

 specimens are quite dingy but this is usually due to superficial 

 foreign matter. Now in the fine specimen of inten-/ij>/n* before me, 



