278 Rev. T. Hincks's Contrihxitions toioards a 



pressed towards the very wide and shallow oral arch ; surface 

 smooth, divided into distinct areas by raised partitions. 

 Grows in rather large tufts, which are rooted by a trunk-like 

 mass of tubular fibres. 



It is difficult, in the absence of living specimens, to form a 

 conjecture respecting the function of the urxinate processes 

 on each side of the cell. They are clearly not to be placed 

 in the same category as the ordinary spines, for they exhibit 

 a very distinctive structure, which points to some special 

 function. Each of them i.s connected with a small sac-like 

 structure, which lies close alongside the margin of the cell 

 between the outer wall and the perigastric cavity. The front 

 wall of the sac rises and becomes somewhat inflated towards 

 the upper extremity, and from this portion the sharp, slightly 

 curved spine springs, extending usually to the base of the 

 oral valve or a little above it. 



The genus Farciminaria is allied, through the structure of its 

 cell, to the Membraniporidffi, from the ordinary type of which 

 it is only distinguishable by its habit of growth and its simply 

 chitinous zocecium. These differences have little systematic 

 value, and have no claim to be made the criteria of a natural 

 division ; but it may be convenient to range the forms which 

 exhibit them as a kind of subgroup of the Membraniporidan 

 family. 



Membranipora, De Blainville. 

 Memh-anipora perfrngilisj MacGillivray (sp.). 

 Biflustra perfrmjilis, MacG. Nat. Hist, of Victoria, Decade vi. p. 27, 



pi. 67. lig. 1. 

 In his account of this species MacGillivray takes no notice 

 of the avicularium, and 1 therefore supply a description and 

 figure of it (PI. VIII. fig. 4). 



Avicidarian cell very narrow, as compared with the ordi- 

 nary cells, elongate, with a calcareous expansion at the bottom 

 as in the latter ; the lower third of the aperture closed in by 

 a membranous wall, the rest occupied by a large horny oper- 

 culum working on a distinct hinge, slightly hollowed at the 

 sides and rounded above (subspatulatej, the margin of the cell 

 a good deal raised round the operculum, and somewhat ex- 

 panded and bent inwards at the points where the sides of the 

 latter are hollowed out. 



The avicularium of this species is an interesting transition 

 form, showing very clearly the morphological relation of the 

 appendages to the normal zocecium. It is not very freely 

 developed in the specimens which I have examined. 



I have not followed MacGillivray in referring the present 



