48 



Meliceritites durobrivensis Gregory. 



Nodelea durobrivensis Gregor}', Cret. Bryoz, p. 310, pi. XIV, figs. 4 — 13. 

 (PI. IV, figs. 1-6, 8.) 



The Zooecia which are divided by well-developed marginal ridges are generally 

 rhombic or hexagonally rhombic, longer than broad, and the very concave suboral 

 area takes up almost half the length of the whole zooecium. No distinct tubercles. 

 The large aperture, which is surrounded by a strongly developed and very often 

 obliquely ascending peristome, is a little longer than broad, and the lateral mar- 

 gins are generally distinctly converging proximally. No distinct oral ledge. The 

 distal half of the aperture together with the peristome generally takes up the whole 

 breadth of the zooecium. The very convex operculum is provided with a distinct 

 flabelliform strialion. 



The Heterozooecia, which in most colonies are present in large numbers, rarely 

 attain the size of the zooecia, and in most cases they are much smaller, sometimes 

 only attaining half the length of the latter. They are rhombic very much concave 

 and provided with a very small about half-elliptical aperture, the larger part of 

 which is covered by a concave lamina, perforated by a narrow fissure, sometimes 

 in the shape of an inverted T. In a number of them I have found an operculum 

 of the same structure as that of the zooecia. Most of them are arranged in longi- 

 tudinal series each consisting of 2 — 7 in such a manner that two succeeding hetero- 

 zooecia are divided from each other by a pair of zooecia. In the more regular 

 cases each two longitudinal series of heterozooecia are divided by two longitudinal 

 series of zooecia, and, therefore, there may be seen on the surface of a fragment 

 as many as 6 longitudinal series of heterozooecia. However, the arrangement as 

 well as the size and the number of the heterozooecia is subject to great variation, 

 and sometimes there may be seen groups of up to 14 adjacent heterozooecia. 



Ooecia have been found. 



No Kenozooecia. 



A Closure by means of a concave lamina is rarely seen. 



The Regeneration takes place in great measure, and the zooecia may be regene- 

 rated either by a new zooecium (figs. 4, 8) or by a heterozooecium (fig. 3). In the 

 latter case the part of the heterozooecium enclosing the aperture may be more or 

 less projecting, and the aperture of the new heterozooecium sometimes forms a 

 right angle with the suboral area. 



The Colonies are incomposite, and the fragments examined are cylindrical with 

 8 — 10 zooecia in each transverse series. I have examined a large number of frag- 

 ments from Chatham (middle chalk) and Fecamp (middle Senonian). 



