10 FREDERICK W. SARDESON 



young, cells may appear at any cell angle, their increase is great- 

 est in the monticules or cell groups. In renewed rapid growth 

 the peripheral monticules tend to develop into branches of the 

 zoarium, but of course all could not. Thus monticules are simi- 

 lar to zoarial branches, but are not branches normally. Branch- 

 ing of the zoarium is due to double region of acrogene growth 

 only. 



The tabulae of Callopora 7nidtitabulata are thin, and the last 

 one is near the cell aperture, and is said to be perforated at the 

 center {vide Eastman, op. cit., f, 456 d) . They are nearly always 

 solid. Right here is the chief supposed basis for the interpreta- 

 tion of Trepostomata as Bryozoa. According to E. O. Ulrich's 

 definition (p. 271, Eastman), each tabula was the perforated top 

 of one zocecium and solid bottom of the next. In fact, the 

 thickened walls here show only that the growth increments 

 lengthening the wall continue on either side downward, thick- 

 ening the wall, and thence as tabulae across the cell opening. 

 Further is not seen. Perforate last tabulae may be incomplete 

 ones. 



The characters for distinction of the species are, therefore, 

 mostly visible on the exterior; the shape of zoarium and its 

 branches, shape, size, and shallow depth of the cells, characters 

 of the monticules, the number, size, and shape of mesopores, and 

 thickness of the wall. All these characters vary, and the varia- 

 tion of all should be noted in learning the species. Extremes 

 may be associated on parts of the same specimen. 



Prasopora simidatrix Ulr. grew upon some solid surface, at 

 first lens-shaped, later conical (PI. A, Fig 7), hemispherical, or 

 irregular, expressing slight tendency to acrogene growth, united 

 with moderate established perigene. A short finger-shaped or 

 a branched sporadic acrogene growth occurs sometimes, and 

 this usually at the center. If the colony died off in part, the 

 remaining part then developed, overspreading the old. Even a 

 symmetrical zoarium could develop from the irregular fragment 

 of another. The cells radiate from the flat or concave lower 



