ulrich-bassler] revision of paleozoic bryozoa 265 



attachment of the zooecia. The fact that the recent forms are erect 

 and the fossil ones parasitic is not of much consequence, since the 

 same difference occurs over and over again between many otherwise 

 closely related genera of Bryozoa. 



Vine (op. cit., 1892) has already pointed out most of the similari- 

 ties of structure existing between Ascodictyon and our proposed 

 Allonema, on the one hand, and the recent genus Valkeria on the 

 other. Our reproduction of one of Hincks' figures of Valkeria uva 

 shows the two features principally relied on in comparing Valkeria 

 with Allonema, namely, the jointed character of the stem and the 

 pores on the segments marking the points where the deciduous 

 zooecia were attached. The form of the zooecial buds and their 

 frequent arrangement in verticils, as in the upper branch on the left 

 side of the figure, are, as pointed out by Vine, extremely suggestive 

 of Ascodictyon. It is to be contended, however, that if the vesicles 

 of Ascodictyon are zooecia, then they must, in all cases observed by 

 us, be only either young or abortive ones. We are inclined to doubt 

 this and to regard them rather as a special kind of zooid, in which 

 case the true zooecia still remain to be discovered. The great varia- 

 tion in size of the vesicles shown by our figures of the known species 

 on plate lxviii, is regarded as supporting the latter view, such a 

 variation in the zooecia appearing quite unlikely to us. 



The various alliances indicated in the foregoing comparisons 

 make it clear that, even in a confessedly provisional classification, a 

 single family should no longer be made to include all the various 

 types now classed as Paleozoic Ctenostomata. Even with the recog- 

 nition of a second family, the Rhopalonariidce, the necessities of the 

 case are not satisfied. Indeed, the need of a third family is only 

 emphasized by the adoption of the second. It might be suggested 

 that if Vinella and the related genus Heteronema are to be eliminated 

 from the Ascodictyonidce, that they be referred to the recent family 

 VesicnlariidcB with which we have compared them. That step, how- 

 ever, seems to us m.ucli more objectionable than the erection of a new 

 family for their special benefit, since it would indicate a degree of 

 relationship that is scarcely warranted by our present knowledge, 

 and certainly a greater one than we are willing to admit at present. 



Under the circumstances the following provisional arrangement of 

 the genera and species seems to us the least objectionable. Time and 

 further research alone can determine whether or not it is based on 

 facts insuring its permanence : 



