280 A. W. AYATEES Olf CHIL0ST03IAT0US BETOZOA FEOM 



c 



the Use of the Opercula in the Determination of the Cheilostomatous 

 Bryozoa "*, I figured the opercnla of some Cellejjorce, and pointed out 

 that the " opercula may assist very much to bring this family out of 

 its present confusion." Mr. Busk took up the idea, when working 

 at the ' Challenger ' Bryozoa, and the results he obtained are of great 

 value ; and I may say that my own collection of opercula indicates 

 that many difficult genera may be brought into order by the study 

 of the chitinous organs. 



The opercula are, of course, wanting in fossils, but the exact know- 

 ledge of the oral aperture thus gained may nevertheless be used. 

 In comparing recent with fossil species it is most important to 

 study the opercula, and in describing this series of Austrahan col- 

 lections such comparison has always been made when possible. 



In the Cellejjorce the shape of the zocecial or vicarious (Busk) 

 avicularia t is of great value ; but I must here repeat what I have 

 already said (Quart. Journ. GreoL Soc. vol. xxxix. p. 424) regarding 

 other genera, namely, that the presence or absence of these avicularia 

 cannot be made a specific character. Among several specimens of 

 recent Cellepora alhirostris from the Semaphore, Adelaide, there are 

 some in which the vicarious avicularia abound ; in one or two I do 

 not find any ; while in other cases, after searching over a large part 

 of the colony in vain, a part is found where ten or twelve may come 

 under the field of the microscope at the same time. Similar condi- 

 tions obtain in recent C. tridenticulata from the same locality, and 

 among the fossils we find the same thing ; for in one large block of 

 this species only one avicularium was found after a complete search 

 among many thousand zocecia. In the present paper the vicarious 

 avicularia are figured of Jlonojwrella sexangidaris. corresponding 

 with those already known from European localities, thus showing 

 that it had been rightly determined before these avicularia were 

 found. Many specimens of Cellaria angustiloba have now been 

 examined ; but it seems that avicularia have only been found in two 

 cases. In the Australian fossil Memhranipora Michaudiana only one 

 has been found. In Microjjorella elevata most interesting lateral 

 zocecial avicularia are now for the first time made known. As 

 bearing upon this subject, it may be mentioned that in reexamining 

 my collection I was surprised to find in Memhranipora Dumerilii a 

 vicarious avicularium, so that here is a case of a common Memhrani- 

 pora in which none have previously been found now yielding an 

 isolated example %. 



Only a short time ago the presence or absence of these organs was 



* Manchester Lit. & Phil. Soc. vol. xviii. p. 8, pi. i. 



t These zocecial avicularia have been named '■' onychocellaria" by Dr. 

 JuUien ; and it is doubtful whether it would not have been better to adopt 

 this than to give a new name. The mandible he then names " onychocelliima." 



+ Mr. Busk, in his paper " On the Use to be made of the Chitinous Organs" 

 &c., describes a slender process rising from the middle of the base of the avicu- 

 larian mandible, and this he terms the " columella," and here and in the ' Chal- 

 lenger' Eeport, p. xix., says that it only occurs in one division of the genus 

 CeUejpora, and in this division " only in those belonging to the southern hemi- 

 sphere." This is by no means the case, as it is to be found in Cellepora 



