778 Transactions of the Society. 



Although it is convenient to commence this study with the 

 separated opercula and mandibles, this should only be considered as 

 an introduction to a complete investigation of the muscular systems 

 of both zooecia and avicularia. Our information with regard to 

 the avicularia is also not complete unless the shape of the openings 

 covered by the mandibles is given ; and this can usually be seen 

 without preparation, but sometimes it is necessary to incinerate * 

 a specimen for the purpose. I would lay great stress upon the 

 examination of this character, as it may be of great value in the 

 determination of fossils, and is one which, a reference to my papers 

 on the Australian Bryozoa will show, can frequently be used; 

 though fossils being as a rule less well preserved than recent 

 material, such work should be based upon the examination of recent 

 specimens. 



Turning to the mandibles figured, those of three Memhrani- 

 ^oras deserve especial attention. One of these is M. Flemingii 

 (fig. 43), from Britain, and great variation having been assigned 

 to this species I was misled into calling a species from Naples 

 M. Flemingii, and another M. Flemingii var., but the former is 

 M. curvirostris of Hincks (fig. 40), and the latter M. tenuirostris 

 Hincks (fig. 41). The mandibles will be found characteristic in 

 each case, but upon examination the same structures are found 

 throughout, the only difierence being in the shape. 



The mandibles of Cellaria sinuosa (fig. 11), Jistulosa (fig. 14), 

 and Johnsoni (fig. 21), though showing considerable characteristic 

 difierences in shape and size, present great similarity in the difierent 

 parts ; and this is the case with other Cellarise. 



In Cellej)ora sardonica (the sub-oral avicularia) (fig. 39), 

 C. digitata (fig. 38), and C. verruculata (fig. 37), the avicularia 

 could scarcely be distinguished except by size. 



The similarity of the small oral avicularia of Smittia Lands- 

 borovii (fig. 16), Porella cervicornis (fig. 18), and Umhonula 

 verrucosa (fig. 19) must at once strike any one. 



On each side of the large mandible of Memhranijpora angulosa 

 (fig. 42) there is a separate thick lunate chitinous mass in the 

 front of the avicularian chamber, and to this the lower corners of 

 the mandible are attached in the position shown. It will be in- 

 teresting to know whether similar structures are the rule where 

 the mandible is very large and powerful. 



In the whole of the Membraniporidee the opercula are very 

 similar, having a considerable lateral projection for the muscular 

 attachments. Mr. Busk's figures of the opercula of Vincularia 

 gothica (loc. cit., p. 72, fig. 2) and F. labiata (p. 73, fig. 3) may 



* A convenient way of doing this is to place the specimen upon a piece of 

 platinum foil and hold it in the flame of a spirit-lamp until all the organic portion 

 is removed. 



