32 BULLETIN 16 5, UNITED STATES NATIONAL MUSEUM 



Between the cellules and without any regular arrangement, are placed, in 

 most colonies, a large number of abortive cellules, of the same shape as the 

 larger ones. In some colonies these abortive cells are full as numerous as the 

 normal ones, and only in a very few instances have we observed colonies to 

 be entirely without them. When the latter is the case, the normal cells are 

 much more regular in size and in arrangement. 



The zooecia are very active, this activity manifesting itself in the 

 presence of numerous regenerated zooecia. But what is most extraor- 

 dinary is to note normal zooecia regenerated by aborted zooecia. 

 It is necessary then to conclude that the latter exercise an important 

 function on the zoarium. We cannot consider them as true aborted 

 zooecia but must believe them to be special cells with different func- 

 tion from that of the various kenozooecia that we know. 



The structure of Membranipora dbortiva is rather different from 

 that figured by Gabb and Horn, 1862, but by reading their text 

 attentively it can be shown that Ulrich and Bassler, 1907, were cor- 

 rect in their interpretation of the species. 



Affinities. — In the nature of its ovicell, the presence of a crypto- 

 cyst, and the place of its avicularia, Menibranipora dbortiva ought 

 to be classed in Amphiblestrum. However, if the presence of vibrac- 

 ula is confirmed, it would be necessary to create a new genus. 



The recent species closest to it is Antropora pustulata Canu and 

 Bassler, 1928, dredged in deep waters of the Gulf of Mexico, in 

 which the ovicell is also hyperstomial and which presents the same 

 kenozooecia ( = aborted zooecia.) The fossil species differs, how- 

 ever, in the place and the nature of the avicularia, which are zooecial 

 and acuminate. This relative identity of exterior aspect seems to 

 confirm the suggestion made for another species that the Vincentown 

 marls may be deposits of relatively deep water. 



The genus Antropora Norman, 1903, has for its genotype Meni- 

 branipora granulifera Hincks, 1880, from Madeira. Hincks did not 

 figure the ovicell, and Norman, 1903, did not mention it but compares 

 this genus with Amphiblestrum. Finally, Harmer refigured Hincks' 

 species with specimens from Malaysia, in which he discovered an 

 endozooecial ovicell and interzooecial (zoarial) avicularia. "We be- 

 lieve that Antropora still requires restudy. 



Herpetopora anglica Lang, 1914, from the English Senonian and 

 Mystriopora mocMeri Lang, 1915, from the English Cenomanian 

 present the same aborted zooecia. These are uniserial species. 



Many fossil and recent Menibranipora frequently have calcified 

 zooecia, which always replace ordinary zooecia. These must not be 

 confused with the aborted zooecia studied here, which have neither 

 regular form nor constant dimensions. Zoology is silent on the 

 anatomy and physiology of all these heteromorphic zooecia, and the 

 paleontologist cannot make useful comparisons. 



