88 Rev. T. Hincks's Contributions towards 



part of the lamina; mandible pointed, directed upward. 

 Ocecia (?). 



Loc. Bahia, on shell (Miss Jelly). 



This form is referred doubtfully to M. trifolium. The 

 cells are smaller than in that species ; the margin is less ele- 

 vated and exhibits no distinct crenature ; the lamina is more 

 strongly calcified. It seems better, however, to rank it for 

 the present as a variety, though the locality may suggest a 

 doubt as to its identity with M. trifolium, which has hitherto 

 only been known as a northern form (Britain, north ; Nor- 

 way ; Arctic Sea ; Labrador). 



Membranipora antiqua, Busk. (PI. XI. fig. 7.) 



Membranipora antiqua, Busk, Quart. Joum. Micr. Sc. vi. p. 262, pi. xx. 

 figs. 1, 2. 



This species is described by Busk as being furnished with 

 vibracula ; but the remarkable appendages which occur, placed 

 on distinct areas, and distributed amongst the zocecia, are in 

 reality avicularia, though of very peculiar structure. The 

 fixed beak is long and somewhat falciform, with a rather 

 broad central groove ; the mandible expanded and subtri- 

 angular at the base, above tapering and setiform. Along one 

 side of the mandible extends a membranous expansion, which 

 is broad and spreading for about two thirds of the length, and 

 narrows off into a mere edging near the top. What the pre- 

 cise use of this curious structure may be it is difficult to say : 

 it certainly renders the appendage quite unfitted for any 

 prehensile work ; but it may make it a more efficient organ of 

 defence. 



The orifice in this species is surrounded by a narrow solid 

 border, and the operculum is fully developed and works on a 

 distinct hinge. 



J o" 



c. With a membranous front wall, the orifice surrounded 

 by a border ; operculum with a distinct hinge. 



Membranipora mamillaris, Lamouroux. 

 (PI. X. fig. 9.) 



Zoacia elongate, rectangular, with membranous front wall, 

 margins thin and smooth ; orifice surrounded by a raised, 

 somewhat thickened border, taller than broad, arched above, 

 slightly narrowed towards the top ; lower margin straight ; 

 operculum with a distinct hinge, of a dark horn-colour ; on 

 each side of the orifice a stout blunt spine, white and lineated 

 longitudinally. Avicularia interspersed amongst the cells, 

 placed at the top of a rectangular area, the fixed portion 



