Polyzoa and Antliozoa from Upper Cretaceous Limestone. 3 



DlASTOPORA COMPRESSA (Goldfuss). 



Plate I., fig. 3. 



1827. Ccriopora compressa, Goldfuss, Petref. Germ., p. 37, pi. xi., 



fig. 4. 

 1851. Ditaxia compressa, von Hagenow, Bry. Maastr. kr., p. 50, 



pi. iv., fig. 10. 



Zoarium of erect bilaminar fronds. Zocecia immersed, and their 

 boundaries not apparent, or very slightly so. Apertures irregularly 

 arranged ; the distance between the apertures in a proximal-distal 

 direction is about once the diameter of an aperture; that in a 

 direction at right angles to the last is once or less than once the 

 diameter of an aperture. This definition does not distinguish D. 

 compressa from Mesenteripora Hyselyi, de Loriol (Urg. Land. : Mem. 

 Soc. helv. Sci. Nat., vol. xxiii., 1869, p. 40, pi. hi., fig. 1), from the 

 Urgonian of Neuchatel ; and from the figures it is difficult to see 

 any difference between these two forms. But fig. 10 m. on pi. iv. of 

 von Hagenow's work shows a piece of a zoarium with the apertures 

 elongate in a proximal-distal direction. It is only described in the 

 legend " Theil der Oberfliiche am oberen Rande," but it looks as if 

 this were a worn surface and the elongation of the apertures were 

 due to the angle between the surface and the direction of the zocecia 

 at that level. It is possible that in M . Hyselyi the direction of the 

 zooecia would be perpendicular to the surface for some distance, in 

 which case a worn specimen would show circular apertures. 



D'Orbigny's figure of Bidiastopora Campichcana (Bry. Cret., 

 1853-4, p. 800, pi. 784, figs. 6 and 8) also resembles Diaspora 

 compressa and Mesenteripora Hyselyi. But Pergens, who has seen 

 d'Orbigny's specimens, identifies B. Campicheana with B. acuta, 

 d'Orbigny, and re-figures the latter (Revision des Bry. Cret. fig. par 

 d'Orbigny, 1890, pi. xi., fig. 7), showing it to be a form quite distinct 

 from D. compressa and M. Hyselyi. 



Gregory places as synonyms of Diastopora compressa the two 

 forms figured by d'Orbigny as Mesenteripora compressa and M. 

 ncocomiensis (Bry. Cret., 1853-4, pi. 756, figs. 10-13 and 7-9) ; but 

 both these forms have emergent zooecia. 



Among the material described the only specimen referable to this 

 species is a small fragment of the base of a frond. The earliest 

 zooecia, as would be expected, differ from the later ones ; they are 

 further apart and slightly emergent. Near the edge of the fragment 

 they are seen to be close together and immersed, with their boun- 

 daries slightly shown. The apertures, especially near the edge, 



