404 ON THE CLOSUEE OF THE CTCLOSTOMATOUS BUTOZOA. 



the cell, and thus important tissues of the colony are kept in 

 healthy contact with the exterior. 



The form of the aperture in the Chilostomata has been recog- 

 nized by all recent authorities as being of the first importance in 

 determination ; and I showed * that the opercula furnish the 

 most reliable specific characters : and these, in the hands of Mr. 

 Busk for Gellepora, and Professor MacGrillivray for Betepora, 

 have given most important results. In all examinations that I 

 have made of fossils the shape of the opercular opening has always 

 been studied where it was .possible ; and in the same way with 

 the Cyclostomata the examination of the shape and size of the 

 aperture and the nature of the closure is likely to extend our 

 knowledge ; and, further, it is only possible to check the natural- 

 ness of classification where many characters are available, for then 

 the correlation of these characters will show when we are upon 

 the right track. Such points as we have been dealing with can, 

 however, only be made available by extended study, and my pre- 

 sent work is not favourable for this ; as with fossils, especially 

 those sent from a distance, there is in many cases only one spe- 

 cimen, whereas there should be abundant material at hand, and 

 in various conditions of growth. 



DESOEIPTION OF PLATE XYII. 



Fig. I. Section oi Badiopora from the Valangian of St. Croix, Switzerland. 



2. Section o{ Hornera concatenata, E.8S.,from the Bartonian of Brendola, 



N. Italy. 



3. Section of Entalophora rugosa, d'Orb., recent, from Naples. 



4. Closure of Eeticulipora dorsalis, Waters, recent, from Naples. 



5. Section of Beticulipora transennata, Waters, in present volume of 



Proc. L. Greol. Soc, fossil, from Australia. 



6. Section of Heteropora {Multicavea) lateralis, d'Orb., from the Senonian 



of Eoyan, France. 



7. Section of part of colony of lAchenopora boUtiformis, d'Orb., fossil, 



from Aldinga, Australia. X 12. 



8. Section of Lichenopora boletiformis, d'Orb. X 7. 



* " The Use of the Opercula," &c. Proc. Manch. Lit. & Phil. Soc. vol. xviii. 

 No. 2, p. 8. 



