ulrich-bassler] revision of paleozoic bryozoa 263 



the difficulty of explaining why they seem to be without clearly 

 defined orifices. A small spot may often be detected that looks dif- 

 ferent from the rest of the swelling, and that most probably repre- 

 sents some kind of orifice, but none of the numerous Specimens 

 before us is in a state of preservation good enough to establish its 

 nature beyond doubt. 



Considering the non-calcareous character of the zooecia of recent 

 Ctenostomata in connection with the fact that the preservation of 

 the zoarium of Rhopalonaria shows that it also was not composed 

 of material favorable to ordinary fossilization, the lack of definite- 

 ness about the zooecial orifice of the fossils may justly be regarded 

 as confirming an alliance with Ctenostomata rather than as purely 

 negative evidence. As a rule, nothing remains of the Rhopalonaria 

 but the peculiar and characteristically arranged, excavated counter- 

 feits of the parasitic zooecia and stolons in the test of the host. Oc- 

 casionally we meet with the fossilized zoarium itself. This is nearly 

 always dark in color and more or less pyritized. Very rarely it is 

 preserved as a siliceous pseudomorph, the silicification of the zoarium 

 having taken place prior to the solution and removal of the calcareous 

 shell in which it was partly imbedded. 



Comparing what we know of Rhopalonaria with recent Ctenos- 

 tomata, we find a striking agreement in the form, connections, and 

 arrangement of the zooecia of Arachnidiiini, of which we present in 

 plates Lxv and lxvi somewhat sketchy copies of figures of two species 

 by Hincks. The zooecial orifice in Arachnidiimi, it will be observed, 

 is small, and (a fact not brought out in our figures), is covered by 

 a pyramid of stout setae forming a closure quite different from those 

 occurring in either the Chilostomata or Cyclostomata. With these 

 minute plates in place, it may be quite readily conceived that even 

 under favorable conditions of fossilization, the position and char- 

 acter of the zooecial orifice of a fossil Arachnidiuni would be obscure. 

 The zooecial orifice in the recent species, it will be further observed, 

 is near the distal extremity of the zooecium. In Rhopalonaria this 

 is not the case, since the possible zooecial orifice in the fusiform 

 swelling is generally much nearer the center. 



Viewing Rhopalonaria as the creeping base of some otherwise un- 

 known bryozoan, the subcentral position of the orifice-like spot 

 becomes significant, for we can now see that it corresponds in all 

 essential respects with the creeping base of a recent Altca. Plate lxv, 

 I, 2, illustrates portions of the base of two species of that genus, A. 

 anguinca and A. truncata, the former showing also some of the 

 erect zooecia. At the attached basal end of the zooecia there is a 



