BRYOZOA. 361 



into any extended discussion of this and other points bearing 

 upon the question,, but as it is an important one, I will men- 

 tion briefly some of uiy reasons for removing the families from 

 the CYCLOSTOMATA. 



First, the zooecia of the FEXESTELLID.E and ACANTHOCLADIID.E 

 are not tubular, but agree closely in form and general structure 

 with those of the PTELODICTYOXID.E and ESCHARID.E.* Second, 

 the primary orifice is drawn out into a shaft-like vestibule, pre- 

 cisely as in typical members of Mr. Vine's new sub-order CRYP- 

 TOSTOMATA. Third, the structure of the secondary deposit over 

 the cells and basal plate, differs in no essential manner from 

 that of the dense tissue which forms the non-poriferous margins 

 aud pointed base of Ptilodictya. and the deposit over the basal 

 portions of the zoaria of many CYSTODICTYOXID.E. Fourth, one 

 or both of the structures that I have called superior and in- 

 ferior hemisepta are usually (perhaps always) present. These 

 four- reasons refer to such weighty points of structure that I 

 am content to rest the question upon them without detailed 

 explanation. The critical student can, without much labor, 

 corroborate at least some of the abundant evidence relating to 

 the points at issue given on the plates attached to this volume. 



(5) ACANTHOCLADIID.E: The minute structure of this family 

 is so much like that of the preceding, that for present needs it 

 is sufficient to point out the features upon which the family is 

 maintained. 



The zoaria are generally pinnate, often fenestrated, and rarely 

 dendroid, differing from those of the FEXESTELLID.E in consisting 

 of primary and secondary branches, and in being without non- 

 poriferous dissepiments. The primary branches are strong 

 straight stems, which usually remain simple, but in a few cases 

 are known to bifurcate. The secondary branches are nearly 

 always considerably smaller than the primary ones, from the 

 two opposite margins of which they are given off. In Syno- 

 dadia and Septopora the secondary branches unite with those 

 of adjacent branches, thus forming reticulate expansions. From 



* In a few species the secondary deposit upon the cells was very slight. These re- 

 semble Chilostomatous Bryozoa in a marked degree. In describing one of these forms 

 (Pinnatovora? simpler* Mr. Vine states (Notes on Yoredale Poly.) that it reminds one of 

 Chilostomatous rather than of Cyclostomatous Bryozoa. 



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