4 



of the other species. They are far less conspicuous, and might easily be passed over by any 

 one vvho was not acquainted vvith the genus. It is probable that this species will hereafter be 

 found on other marine objects collected during the Expedition. The tubes contain large numbers 

 of the zooids, in a good state of preservation, together with buds and embryos. All the zooids 

 are female. It is specially noteworthy that this specimen was collected between tide-marks, 

 Cephalodiscus having previously been regarded as an abjssal animal. 



C. sibogae n. sp., (PI. I, fig. 2) is also represented by a single specimen, which was 

 growing on a small rock. It is a more conspicuous object than the last species; and it had 

 been placed in a bottle by itself and sent to me as a Polyzoon. Although the zooids are 

 unfortunately not well preserved, their state was sufficiently good to enable me to make out some 

 interesting facts with regard to the males, and in particular to demonstrate the occurrence, in 

 Cephalodiscus^ of an extraordinary sexual dimorphism. The male individuals (PI. VII, figs. 72 — 76) 

 are entirely unlike the females found in other species, being without tentacles and possessing 

 only a vestigial alimentary canal. They are accompanied by neuter individuals (PI. I, fig. 3), 

 which, except in possessing no reproductive organs, have the typical Cephalodiscus-?,iY\iQ.iv\rQ. 

 These neuters probably perform the functions of digestion and nutrition for the entire colony. 

 No females are present, and the possibility is not excluded that C. sibogae is the male form 

 of C. gracilis. 



C. levinseni n. sp. This species (PI. I, fig. 10), the property of the Copenhagen Museum, 

 was most generously placed in my hands for description by Dr. G. M. R. Levinsen. On first 

 finding Cephalodiscus among the "Siboga" material, I wrote to Dr. Levinsen, to enquire whether 

 he was working at a specimen belonging to this genus which, as I had been informed a year 

 or two previously, was in his possession. It appeared to me not improbable that it might belong 

 to the same species as one of the "Siboga" forms. With the utmost generosity, for which I 

 desire here to express my most cordial acknowledgment, Dr. Levinsen replied by sending me the 

 specimen, and asking me to investigate it with the other material in my hands. It is in many 

 respects a very remarkable species, differing in the clearest way from all the others. The zooids 

 are all female, and numerous embryos are present. 



The British Museum have recently received other specimens of Cephalodiscus, of which 

 descriptions will doubtless be published in due course. 



III. DIAGNOSES OF SPECIES OF CEPHALODISCUS. 



The most useful specific characters of the genus Cephalodisctis appear to me to be 

 afforded by the coenoecium, the proportions of the body and stalk of the zooids, the number 

 of tentaculiferous arms, and the presence or absence of vesicle-bearing end-bulbs on the arms. 

 The species which have come under my notice can readily be discriminated by these features, 

 but in the short diagnoses which follow I have made some use of other characters, such as 

 the profusion with which buds are produced. Since the diagnosis depends, in each case, upon 



