EAELY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 



101 



Tliey are most apparent in the latter because more opportunity is 

 afforded to show them as they pierce the walls. However, these 

 pores do not differ from the usual pores seen in other ceramoporoid 

 genera, so that their occurrence can not be considered as an important 

 generic characteristic. The minute structure of the zooecia in F. 

 interpuncta, the style of lunarium, arrangement and occurrence of 

 mesopores, is precisely the same as in Bythotrypa laxata, the genotype 

 of Bythotrypa. Moreover, each species has the same internal struc- 

 ture, particularly the loose, irregular, vesicular tissue formed by 

 mesopores. 



Ulrich has given a clear, concise definition of Bythotrypa which I 

 quote, as it applies without change to the genotype of Favositella. 



Fig. 35.— Favositella interpuncta. a, veetical section, X20, showing the loose vesiculae-like 



TISSUE DEVELOPED IN THE MATURE REGION, THE POEES CONNECTING ADJOINING ZOCECIA AND AN ESfCLUDED 

 concentric body at c; b, tangential section, X20, with STEUCTURE of ZOffiCIA AND MESOPOEES AND 

 ONE OF THE INCLUDED SILICEOUS BODIES AT C. WENLOCK SHALE, WeNLOCK, ENGLAND. 



Zoaria massive or lamellate. Zocecia forming long continuous tubes, intersected 

 by thin diaphragms, their walls minutely crenulate and with the structure character- 

 izing the ceramoporoids. Lunarium well defined, large, projecting above the rest of 

 the aperture margin. Mesopores numerous, open at the surface, interiorly forming a 

 species of vesicular tissue imusually loose and irregular in construction. 



The loose, irregidar vesicular tissue formed by the mesopores is the 

 character most relied upon in separating species of Bythotrypa, or, 

 as they should now be designated, Favositella. This tissue is similar 

 to the vesicular filling of the interzooecial spaces in the Fistuliporidse. 

 As remarked by Ulrich, Bythotrypa represents probably a premature 

 evolution of the fistuliporoid type that either became extinct or was 

 reabsorbed into the parent stock. The Silurian occurrence of the 



