110 Descriptions of JS r eiu } or Little Knoivn, Polyzoa. 



the articulation of the mandible, is very small, membranous, 

 and triangular. The specimens present an extraordinary 

 development of spines. These are situated along the 

 posterior edges of the zoarium, are directed upwards, back- 

 wards, and inwards, and are divided into numerous long, 

 nearly straight, sharp branches. They are not noticed by 

 Hincks, and as the specimens agree with his figure and de- 

 scription in other respects, I think they can only be varietal, 

 and cannot consider them as of specific value. 



Family Membranipomd,e. 

 Membranipora bimamillata, n. sp. Plate II. ; fig. 2. 



Zoarium encrusting. Cells elongated, quadrate, separated 

 by raised margins. Aperture elliptical, the edge formed by 

 a thickened, crenulated rim ; the lower part of the aperture 

 occupied by a large plate or denticle, sloping backwards and 

 usually with a fissure or notch on one side. Front of the 

 cell formed by a calcareous, granulated lamina, sloping- 

 inwards to the aperture. At the lower part of the cell are 

 two rounded prominences or mamillge, or occasionally only a 

 single, transversely elongated mass. 



Portland, Mr. Maplestone. 



The broad, smooth plate at the lower part of the aperture 

 is evidently of the same nature as the serrated denticle of 

 Biflustra delicatula, with which, and M. papulifera, this 

 species is closely related. 



Membranipora porcellana, n. sp. Plate II., fig. 3. 



Cells small, quadrate, separated by distinct, narrow, raised 

 margins; upper part membranous; lower part occupied by a 

 large, smooth, white elevation ; a short, thick, rounded pro- 

 cess ou each side at the upper angle. 



Portland, Mr. Maplestone. 



The cells in this species are very peculiar. They are 

 quadrate, separated by narrow, raised margins. The upper 

 half is membranous, the membranous front being situated at 

 a considerable depth, with the flap-shaped mouth at the 

 upper end. The lower half is prominent, smooth, white, 

 calcareous, rising higher than the separating margin. The 

 upper part of the cell is in the form of a broad, shallow arch 

 hollowed out in the base of the prominent portion of the 

 cell above. 



