1921.] A. Robertson: Report on Bryozoa. 43 



smaller branches, the finest rootlets clasping minute objects in 

 the substratum. 



In so far the characters of the K. arabianensis, while differing 

 somewhat from other members of this genus, do not remove it 

 from the familj' Bicellariids; to which Kinetoskias and the Bugulas 

 belong. The two characters remaining to be discussed, viz. 

 sessile avicularia and the peculiar structure of the ooecium are 

 both unknown in that family. The former is a distinguishing 

 mark of the family CeUulariida^ and except in a slight dift'erence 

 in position the sessile avicularia on the Arabian species are similar 

 to the lateral avicularia found on such Cellularians as Menipca or 

 Scrupoccllayia. 



The unique ooecium of this species reveals a wholh- unexpect- 

 ed dimorphism previously unknown in either of the two families 

 mentioned above and only rarely occurring in t!ie Cheilostomes. 

 The only other Cheilostomatous bryozoan which shows a similar 

 condition is Adennella and its congeners where a trimorphism 

 exists, resulting in nutritive zocecia, reproductive or ooecial zoitcia, 

 and zooecia transformed into avicularia. In Ciisia, a Cyclostome, 

 there is found a dimorphic condition quite similar to that which 

 obtains in K. a>abianensis, in which a zocecium grows to an 

 unusual size and takes on the reproductive instead of the 

 nutritive function. Unlike the ooecium of Crista which never 

 assumes the nutritive functions, the species found in the Arabian 

 Sea first performs- the nutritive function, indicated by the presence 

 of a polypide, and only secondarily assumes the ooecial func- 

 tion. 



The ocecial condition most nearly resembling that shown by 

 K. arahianensis is found in Cellularia cirrata, Busk (1884). " The 

 ooecium," as Busk remarks, "is formed by an entire metamor- 

 phosed zocecium, with a wide opening closed by a broad valve 

 having a semilunar chitinous border." At first glance, the occur- 

 rence of ocecia so unusal in structure and yet so similar externally 

 would lead one to suspect close relationship between C. cirrata 

 and the present species. And indeed for a time the two were 

 thought to be identical. This opinion was strengthened by the 

 facts that both are abyssal and both come from regions geographi- 

 cally similar. Busk, however, makes no mention of internal 

 structure, but remarks that the material was in poor condition 

 and much curled. He evidently found no articulated avicularia 

 and no parietal muscles, and the characters which his specimen 

 disi losed justified him in placing it in the Cellulariida^. How- 

 ever he expresses a doubt that he is correct and remarks that 

 perhaps a new genus should be established to receive his species. 

 The occurrence of this peculiar orecium in these two species leads 

 one to wonder if C. cirrata and the species from the Arabian Sea 

 are identical, especially when one reflects that the curled condition 

 upon which Busk remarks might be caused by the contraction of 

 parietal muscles and at the same time might make the detection 

 of these muscles impossible. 



