noo 



i\lr. F. J. North on the 



adovally, ami acuminateil adapically. It is 4 mm. long and 

 2'75 mm. wide. 



Tlie anal aperture, whicli is rather less than 0*5 mm. in 

 diameter, is situated on the adoral half of the long axis 

 of the periproct, and since the whole sj^stem is adapicall}"- 

 situated, the anus is ju^it midway between the ambitus and 

 the oral opening. It is raised sliglitiy above the plane of the 



A, 13, C, D. Discoidea ajlindrica (Lamarck), Upper Chalk, Swaftham, 

 Norfolk. In (ieol. Dept., National Museum of Wales. 

 Reg. no. l.>. loG. G. 8. 



A. Profile {jt, periproctal system), nat. size. 



B. Plan of adoral surface (??i, mouth-opening), nat, size. 

 0. Periproctal plates, x 12. 



D. Ditto, side view (a, anal aperture), x 12. 



E. Periproctal plates of Discoidea minima, Agassiz, enlarged (after 

 Wright). 



adoral surface of the test, and is surrounded by the peri- 

 l)roctal plates, which slope from it in all directions, giving 

 the whole system the appearance of a low boss (text-fig., A.p 



The periproctal plates are nineteen in number, arranged 

 in two cycles of nine plates each, with one odd pentagonal 



