98 R. M. Brydone — New Chalk Polyzoa. 



many points of resemblance (apart from the Cribriline surface) to 

 some of them, e.g. M. thoraceformis aud M. Shaivfordensis that it 

 seemed bound to be a member of that group with a complete 

 secondary front wall. I have not, however, been able to find any 

 trace of Cribriline structure about it. It seems to lead almost 

 directly to 



Cellepoka. (?) DiASToiDES, sp. uov. (PL YI, Fig. 4.) 



Zoarium incrusting, consisting of a common crust out of which 

 arise long tubular, slightly barrel-shaped zooecia, free for the greater 

 part of their length, inclined strongly forwards but sometimes 

 turning erect at the end ; they have slightly thickened peristomes, in 

 which there may be from one to three pores, one in the middle of 

 the posterior part being fairly regular ; these pores can often be seen 

 in the larger zooecia to be the apertures of tubuli mainly embedded 

 in the zocecial wall ; the apertures are more or less circular, but 

 sometimes very irregular in shape : the ooecia are very small, 

 globose, perched on the anterior part of the peristome and over- 

 hanging the greater part of the aperture : there is a partial fringe 

 of shallow Membraniporiform zooecia. 



This species is fairly common at Trimingham, and is probably to 

 be found in the Norwich Chalk, as I have specimens from Norwich 

 and Weybourne which seem to be inchoate forms of this species. 

 It is so clearly in most respects a development fi'om Pseudostege 

 concursa (ante) that it is rather surprising that there should be 

 no trace of vicarious avicularia. Apart from the ooecia and the 

 peristomial pores it might easily pass for a sturdy Dtastopora. 



i;. -H. * 



There is a large group of Memhraniporce in which a pair of pores 

 or tubes at the anterior end are repeated with great regularity and 

 another group in which a single tubular prominence occurs very 

 persistently at the posterior end of the aperture. Both are well 

 represented in the English Chalk, and they might be expected to be 

 always easily distinguishable, but this is not the case. I propose to 

 deal with some of the English species of these groups in order of 

 seniority. 



Membranipoka Seafordensis, sp. nov. (PI. VI, Figs. 5, 6.) 



Zoariwn unilaminate, normally incrusting, occasionally free. 



Zooecia of medium size, average length -5 to '6 mm., breadth -4 mm., 

 with thin common side-walls ; apertures naturally widely oval, but 

 rendered irregularly polygonal by intrusion of the edges of the more 

 or less rounded protuberances, with small round or elliptical apertures, 

 of which a pair is set with extreme regularity on the front wall of 

 every zooecium anteriorly to the ooecium ; these protuberances 

 appear to be accessory avicularia of the small beak-shaped type in 

 a primitive stage ; sometimes they become confluent. 



Ooecia occur with very great regularity : they are set on a shelf so 

 deep within the aperture at the anterior end that their tops are little 

 more than flush with, or may even be below, the general surface; 

 their apertures appear to be very strongly cut back, so that the 

 visible top is very much shorter than the basal shelf : the latter is 



