328 



A. W. WATERS ON FOSSIL CHILOSTOMATOTJS 



are provided with a lid or "beak," they may still longer render 

 assistance to the colony ; for the polypide of a cell may be dead, 

 and the cell itself covered with mud, but yet the zoarium may be 

 living, and under favourable circumstances a new polypide may 

 grow in this very zooecium. 



Modifications may take place, and the avicularia become highly 

 differentiated, until we find them occupying the place of a zooecium 

 and of equal individual value with the zooecia. Tracing it thus 

 from below instead of from above, as is usually attempted, we get 

 a much more reasonable explanation of the origin and function of 

 the avicularia; for certainly when we find very minute avicularia 

 on the root, and on the back of the zoarium, besides large numbers on 

 the front of the cell, the prehensile theory seems utterly to fail ; and 

 although the present idea requires further development, yet the 

 examination of living forms seems to furnish much to support it. 



Smitt points out that in Nellia oculata, B., the papilliform pro- 

 cesses are avicularia, sometimes with and sometimes without covers 

 (mandibles) ; and we are constantly meeting with similar instances. 



Mr. Hincks has kindly furnished me with an advance plate and 

 description of Oribrillina tuhulifera, Hincks (see Ann. Nat. Hist., 

 July 1881, p. 8, pi. i. fig. 7), to which the present is closely related. 

 The only important difference seems to be the relative size of the 

 oral aperture, which is very small in the fossil. The specimen now 

 described is very small ; and it is to be hoped that a larger specimen 

 may be found, upon which the affinities can be more exactly studied. 



28. Mtjcronella mtjcronata, Sm. Plate XVII. fig. 66. 



LJscharipora mucronata, Smitt, Floridan Bryozoa, p. 24, pi. v. 

 figs. 113-115. 



? Eschar a Liversidgei, T. Woods, " On some Tertiary Australian 

 Polyzoa," Tr. Roy. Soc. New S. Wales, 1876, p. 3, figs. 11, 12, 13. 



Zooecia obscure, slightly elevated ; aperture rounded above, straight 

 below, with a mucro or broad, flat, plate-like expansion in front of 

 the proximal edge ; on the front of the zooecia usually five large 

 pores partially closed by a large, simple or bifurcate denticle, some- 

 times only three or four large pores, when there is usually a small 

 rudimentary pore. Angular avicularia at the sides of the zooecia ; 

 the two are usually unequal in size ; a minute avicularium in the 

 aperture. Probably incrusting or Hemeschara-form, from Yarra- 

 Yarra. Aperture 0*23 mm. wide. 



In the Mount-Gambier specimens in the Lond. Geol. Soc. collec- 

 tion there are usually only three pores, but sometimes four or five ; 

 and although the avicularia are not so distinct, and were not figured 

 or described by Mr. Woods, yet they are to be seen at the sides of 

 the zooecia. 



Loc. Living : W. off Tortugas, Florida. Fossil : Mount Gambier 

 (Woods and Lond. Geol. Soc. coll.). 



29. Mtjcronella dtjplicata, sp. nov. Plate XVI. fig. 54. 



The fragment is small ; but some characters are shown which are 



