EARLY PALEOZOIC BRYOZOA OF THE BALTIC PROVINCES. 



199 



are a tube diameter distant in the most crowded part and tliree or 

 four times that distance from each other in the immature region. 

 Still another difference is the presence of small acanthopores in 

 M. egena, but these are so inconspicuous that they can be distin- 

 guished only in thin sections. The size of the zooecia and the tabu- 

 lation of the mesopores is practically the same in both species. 



In spite of the great similarity to the preceding species, the present 

 form is believed to be more closely related to the type of the genus, 

 Mesotrypa injida (Ulrich) , from the Black River shales of Minnesota, 



Fig. 107.— Mesotrypa egena. a, side view of type-specimen, natukal size; l, tangential section 



THROUGH THE MATURE ZONE, X20; C AND d, PORTIONS OF THE SAME, X35, SHOWING WALL STRUCTURE 

 AND VARIATIONS IN NUMBER OF ACANTHOPORES; 6 AND /, TWO PORTIONS OF A VERTICAL SECTION, X20. 



Kegel beds (D2), Habbinem, Esthonia. 



on account of the presence of small acanthopores and the numerous 

 curved diaphragms. The acanthopores are much stronger and the 

 diaphragms more curved in M. injida, but certain portions of its 

 zoarium sometimes exhibit a structure resembling that in M. egeTia. 

 Indeed, the latter may represent merely a poorly developed stage of 

 M. injida. 



Occurrence. — Rare in the Kegel limestone (D2) at Habbmem, 

 Esthonia. 



Hohtype.— Cat. No. 57283, U.S.N.M. 



Two thin sections of the type-specimen are in the British Museum 

 collections. 



