ABT. 22. CYCLOSTOMATOUS BRYOZOA — CANU AND BASSLER. 



67 



Sti^cture. — In longitudinal section the tubes are cylindrical with 

 dorsal gemmation occurring on a thick layer of nematopores. The 

 latter are long, rectilinear with very thick walls. The section in 

 this species is absolutely identical with that of Truncatula suhpinnata 



Fig. 13.— A-E. Truucatula tetragona Michelin, 1846. 



A. Transverse section, X 12, cutting the narrowest part of a brancli between 

 two pinnules and sliowiug the tetragonal form. 



B. Transverse section, X 12, passing just below a pinnule. 



C. A meridian section, X 12, cutting the axis of development and shewing 

 the central tube. 



D. Meridian section, X 12, through the dorsal, cutting the young stages 

 of the nematopores, the tubes of which are indicated by the lozenge-sliaped 

 areas. 



E. Longitudinal section, X12, through a branching specimen in which the 

 lozenge-shaped areas indicate the point of bifurcation The dorsal with its 

 nematopores is to the left. 



Cretaceous (Turonian) : Ruille Ponc6 (Loir-et-Cher), France. 

 F-I. Truncatula suhpinnata D'Orbigny, 1854. 



F-H. Three transverse sections, X 12, at different heights in the branch and 

 showing the thick dorsal zone penetrated by the nematopores. 



I. Longitudinal section, X 12, illustrating the structure of the dorsal with 

 its nematopores to the left, and the frontal to the right. 



Cretaceous (Cenomanian) : Le Mans (Sarthe), France. 



D'Orbigny, 1854. In transverse section the dorsal is very thick and 

 perforated by nematopores. The tubes are quite numerous, small; 

 their diameter increases toward the frontal; the smallest pores are 

 the nematopores. The meridian section shows the normal develop- 

 ment of the tubes above the layer of nematopores in the axis of the 



