R. M. Brydone — Chalk Polyzoa. 197 



iufolds of the side walls. JEschara Lesueuri, Hag., sp.,^ is a good 

 example, and others have been figured by D'Orbigny. Similar forms 

 are not uncommon in the English Chalk, but it is curious that all 

 the foreign forms seem to be of branching Biflustrine habit, while 

 all the English species I have yet met with form unilaminate sheets. 



Membeanipoea Geavensis, sp. nov. PI. YII, Eigs. 1, 2. 



Zoarium unilaminate, always adherent. 



Zooecia large, subpyriforra, with distinct side walls and a variable 

 amount of internal front wall, in consequence of which the areas vary 

 from slightly elliptical to practically semicircular, but the lower lip 

 of the area never becomes convex. 



Ocecia helmet-shaped, large and wide, with a gently convex free edge. 



Avicularia about half as long again as the zooecia ; above the 

 constricting prominence they possess fairly definite side walls and 

 front walls ; these side walls thin away against the adjoining zooecia, 

 and their bounding sutures are very hard to trace ; the front walls 

 are fairly wide and very deep-set at the head, but narrow gradually 

 and rise steadily towards the middle ; the infold of the side wall 

 starts a long way below the level of the upper end of the area, is bold 

 and runs with a slightly convex edge obliquely inwards until it 

 overlies the edge of the rising front wall, and then the two edges 

 appear to run together, meeting a little further dowQ and inwards ; 

 the junction is made into a small, rather brittle, projecting point by 

 the sharp cutting-back immediately below it of the upper part of the 

 mass, which then passes rapidly into a rounded side wall with 

 a steeply sloping inner surface, which flattens out until at the 

 foot the avicularium is subpyriform like the zooecium ; the area is 

 naturally marked olf by the constricting prominences into an upper 

 and a lower section, the upper being much the larger. Avicularia 

 are rarely developed until the zoarium has attained a considerable 

 size, and it is therefore difficult to distinguish small zoaria from the 

 mass of featureless specimens which it is customary to identify with 

 some simple living Ifemhratiipora, but which are probably incapable 

 of satisfactory identification. 



This species is at present known to me only from the zone of 

 M. cor-anguinum at Gravesend, where it is rather scarce. 



Membeanipoea Spaeksi, sp. nov. PI. YII, Eigs. 5-8. 



Zoarium unilaminate, always free and foliaceous. 



Zooecia normally hexagonal and equilateral, with well-marked 

 boundary sutures, thick flat walls, and slightly elliptical areas, but 

 very variable at times both in shape and size ; at the head of the 

 zooecium there is suddenly developed a narrow deep-set internal front 

 wall, which is very characteristic. 



Ooecia rare, but strong and well preserved, helmet-shaped and 

 wide, with a free edge only slightly concave. 



Avicularia very sparse in occurrence, of the same general type 

 as in J/. Oravensis, but with a strong tendency, both in external and 



■^ Hagenow, Die Bryozoa der Maest. Kreideb., p. 72, t. viii, fig. 17, and 

 t. xii, fig. 12. 



