NORTH AMERICAN EARLY TERTIARY BRYOZOA. 707 



Affinities. This species is very close to Crisia hornesi Reuss. 1847, in the dis- 

 tance between its tubes, which is less than the zoarial width. It differs from it 

 simply in the smaller micrometric measurements. 



We dedicate this species to Mr. E. N. Lowe, State geologist of Mississippi, to 

 whom we are indebted for many courtesies. 



Occut^rencc. Lower Jacksonian (Moodys marl) : Jackson, Mississippi (very 

 rare). 1 



Holotypc.Cnt. No. 65338, U.S.N.M. 



Genus CRISIDIA Milne-Edwards, 1838. 



1838. Crisidia MILNE-EDWARDS, Memoire sur les Crisies, les Hornfires et plusieurs 

 autres Polypes, Annnles des Sciences Naturelles, Zoologie, ser. 2, vol. 9, p. 11. 



The zooecia are uniserial. 



Genotype. Crisia (Sertularin) cornuta Ellis, 1755. 



Range. Miocene-Recent. 



This genus has not been recognized, but we are ignorant of the reasons. We 

 have recognized it in the application of our fundamental principle : the genus is a 

 natural one when any function operates in a different manner. Here the gemma- 

 tion is different and more simple than in the genus Crisia Lamouroux, 1816. 



Family PLAGIOECIIDAE Canu, 1918. 



The longitudinal axis of the ovicell is perpendicular to the zooecial axis. 

 The ovicell is formed before the calcification of the neighboring tubes, the forma- 

 tion of which it hinders. The oeciostome is small. 



This family is quite well characterized by the orthogonal development of 

 the ovicell. In all the other families this development is directed parallel to the 

 zooecial tubes. The generic divisions are hard to determine because of the variations 

 of the oeciostome which is always difficult to discover as it is so small or so much like 

 a tube. Often it is only by dissection of the ovicell that the oeciostome may be 

 found with certainty; unfortunately the ovicelled specimens are still too rare in 

 collections. 



The principal known genera are Plagioecia Canu, 1918, and Desmeplagioecia, 

 new genus. However, it is certain that the first of these genera will be dismembered 

 later according to the function of evacuation of the larvae. 



Genus PLAGIOECIA Canu, 1918. 



1918. Plagioecia CANU, Les ovicelles des bryozoaires cyclostomes, Bulletin cle la Socit6 

 Geologique, France, ser. 4, vol. 16, p. 327. 



The ovicell is transversal. The oeciostome is small, equal to or less than the 

 zooecial diameter. The tubes are isolated from each other. No adventitious tubes. 



1 We have found segments of Crisia in the Claibornian at Claiborne, Alabama, which are close to Crisia 

 subaequalis Reuss, 1869, but which are, however, very poorly preserved. We have also found very beautiful 

 specimens in the Vicksbnrgian, but unfortunately they were broken in transit through the mails. 



