104 



BULLETIN 11, UNITED' STATES NATIONAL MUSEUM. 



number of intervening mesopores. The mesopores are usually small, 

 irregular in shape, and few in number. Both zooecia and mesopores 

 have tliin walls which have the indefinite structiu-e characteristic of 

 the Ceramoporidse. The lunarium is ill-developed in some of the 

 zooecia and at best it appears only as a thickened border occupjdng 

 the posterior fourth of the zocecial walls, and with its ends not pro- 

 jecting into the zooecial cavity. Where the lunarium is apparently 

 absent, its place is indicated by the regularly curved form of the 

 zocecial wall, the opposite portion of the zooecium being angular or 

 less uniformly curved. Sometimes additional layers of light-colored 

 tissue are deposited upon the lunarium, adding to its distinctness in 

 tansrential sections. 





iMMmw". 



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Fig. 37.— Favositella discoidalis. a and 6, top and side views of a zoarium, natural size; c, sur- 

 face OF SAME, X9; d, TANGENTIAL SECTION, X20; e AND/, VERTICAL SECTION, X9, ILLUSTRATING SLIGHT 

 VARUTIOfT IN STRUCTURE. ECHINOSPHERITES LIMESTONE (CI), KATLINO, GOVERNMENT OF ST. PETERS- 

 BURG. 



The characteristic loose vesicular structure is somewhat incom- 

 pletely developed in the present species, mainly because of the small 

 size of the zoarium. It is clearly indicated, however, in the vertical 

 sections figured. Thin diaphragms are developed in the tubes at 

 intervals slightly greater than their own diameter. 



The present form is probably most closely allied to Favositella 

 laxata (Ulrich), which holds approximately the same stratigraphic 

 position in America. Favositella laxata differs, however, first in 

 forming quite large zoaria, second, in having smaller zooecia (the 

 average zooecium being 0.4 mm. in diameter) , and, finally, in possessing 

 more numerous mesopores. The tabulation and other internal fea- 

 tures of both species are practically identical. Compared with asso- 



