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BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



often preserving the impression of the object upon which growth 

 started. Continued unequal development in certain parts of such 

 regularly formed zoaria result in the irregular masses figured by 

 Dybowski (pi. 5, fig. 3). An irregular mass with two conspicuous 

 horn-like projections was selected as the type of Dianulites hieornis 

 by Eichwald. In some cases two normally shaped zoaria may be 

 joined, the base of the younger adhering to the top of the older speci- 

 mens, or, again, curious double forms may occur by continued growth 



Fig. 197.— Diplotetpa bicornis. a, vektical section through the basal part of a zoarium, X20, 



SHOWING THE OUTER PORTION OF THE MATURE REGION OBSCURED BY DEPOSITS OF TISSUE; b, SMALL POR- 

 TION OF THE SAME SECTION ENLARGED TO EXHIBIT DEPOSITION OF TISSUE MORE CLEARLY; C, A TANGENTIAL 

 SECTION, X20, PASSING FROM THE REGION OF NORMAL ZOCECIA AND MESOPORES INTO THE AREA OF APER- 

 TURES WITH GREATLY THICKENED WALLS. THE ORDINARY INTERNAL STRUCTURE OP THIS SPECIES IS 

 SHOWN IN FIG. 198, DRAWN FROM THEN SECTIONS PREPARED FROM THE SAME SPECIMEN GmNG THE STRUC- 

 TURE FIGURED ABOVE. JEWE LIMESTONE (Dl), BARON TOLL'S ESTATE, ESTHONIA. 



of certain zooecia of a lower zoarium into a second more or less regular 

 example. Cellufiferous surface usually smooth, but in a few exam- 

 ples the maculae have been observed to form low rounded monticules. 

 Zooecial tubes polygonal, five to six in 2 mm. Mesopores of vari- 

 able size and number, most numerous in the maculae where they 

 isolate the zooecia. Walls of both zooecia and mesopores thin in the 

 immature zone and in the mature region of the younger stage of a 



