BRYOZOA. 347 



deposit. Here the vertical plates between which the primitive 

 cells are arranged are also obsolete, although they may still be 

 represented at the surface by ridge-like elevations. A complete 

 peristome usually surrounds the superficial aperture, but some- 

 times the lunarial side only is elevated. A peculiar feature 

 about the lunarium is that it is always directed away from the 

 non-poriferous margins. 



In internal structure and zocecial characters the various 

 forms of this family show great uniformity, so that we are 

 forced to rely almost solely upon zoarial peculiarities in draw- 

 ing the generic divisions. Fortunately these are very constant, 

 and, being conspicuous, readily serve the purpose of classifica- 

 tion. 



The affinities of the family are with the FISTULIPORID.E on the 

 one hand and the STICTOPORID.E on the other. Pachydictya, has 

 all the characters of the CYSTODICTYONID,E, excepting the luna- 

 rium, and it seems highly probable that they had a common 

 origin. The FISTULIPORID.E, however, approach closest in their 

 later representatives (e. g. Meekopora), a fact apparently indi- 

 cating that the agreement is due to the moulding influences of 

 surrounding conditions rather than to ancestral relationship.* 



(2) STicTOPORir.E: The bifoliate zoaria of this important 

 family formed compressed, dichotomously dividing, continuous 

 or segmented branches, or palmate or leaf-like expansions. The 

 primitive cell is subquadrate, and with or without superior 

 hemiseptum. The inferior hemiseptum and mesopores are ap- 

 parently always absent, but vesicular tissue is sometimes pre- 

 sent. The median tubuli between the divisional laminae are 

 probably to be regarded as the most important peculiarity of 

 the family, though their true nature and functions have not yet 

 been determined satisfactorily. Likewise the granular termina- 

 tions of the vertical tubuli, (which I believe to have communi- 

 cated with those between the median laminae and to have 

 formed part of a system of communication between the pri- 

 mary cells and the external surface,) are more or less conspicu- 



* Many instances might be mentioned to show that like surroundings are apt to 

 produce similar variations in really widely different organisms. For instance, in the 

 Cincinnati group at Delafleld, Wis., where mouticuliferous TBEPOSTOMATA prevail, several 

 species occur that are represented by nearly smooth forms in the Ohio exposures of 

 the same formation. At the Ohio localities the mammulated forms are comparatively 

 less abundant. 



