ART. 22. CYCLOSTOMATOUS BRYOZOA CANU AND BASSLER. 



109 



their extremity. There are numerous diaphragms. The mesopores 

 are rather numerous in the tangential sections and smaller than the 

 tubes. In the longitudinal sections they appear of the same diameter 

 as the tubes and are rarely oriented in the same direction ; this re- 

 sults in a complex structure on the zoarial margins which is very 

 difficult to interpret. This phenomenon is not rare, and we have al- 

 ready observed it in Reteporidae ; this is the characteristic of diver- 

 gent mesopores. 



Fig. 31. — Tretocycloecia dichotoma Reuss, 1847. 



A. Portion of a transverse section, X 12. 



B. Longitudinal section, X 12. 



Miocene (Helvetian): Dou§-la-Fontaine (Maine-et-Loire), France. 



The tubes and the mesopores are polygonal; their walls are not 

 vesicular. 



The ovicell is orbicular, little deep, placed on the mesopores. It is 

 perforated by a certain number of tubes accompanied by a row of 

 mesopores. The oeciopore is submedian and of a diameter smaller 

 than that of the tubes. 



The zoarium is often formed of many successive lamellae of zooe- 

 cia. The enveloping lamella is capable of covering the ovicell itself, 

 the fragile wall of which is thus preserved and may be rediscovered. 



The peristomes are little salient. On the zoarial surface they are 

 often grouped in radial rows around a hypothetic center. 



In spite of its exterior appearance, this species is not Cerlopora 

 dichotoma Goldfuss, 1827. Not only the ovicell is quite different, but 



