54 BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



DESCRIPTIONS OF GENERA AND SPECIES. 

 Order CTENOSTOMATA Busk. 



The Paleozoic fossils referred to this order of the Bryozoa have 

 been made the subject of a small monograph ^ to which the reader 

 is referred for a more detailed discussion than can be given at present. 

 As remarked in that work, httle is known about these peculiar types 

 of fossil Bryozoa, and, while their classification with the Ctenostomata 

 is perhaps a little better than a mere working theory, it rests mainly 

 on highly suggestive resemblances between the fossil organism and 

 the supposed corresponding parts of living forms, and on conjectures 

 as to the unknown parts. Again, their reference to the Ctenostomata 

 is supported by more and stronger arguments and opposed by fewer 

 objections than when comparison is made with any other class of 

 organisms. As these fossUs are comparatively rare in American 

 strata, which have been searched quite thoroughly for them, it is 

 not surprising that only a few specimens have been found in the 

 Russian and Swedish deposits. However, the few examples that 

 have appeared in the various collections studied have been fairly 

 well preserved and their identification with American forms can be 

 made with a correspondingly greater degree of certainty. 



With a possible exception, the various species referred to as Paleo- 

 zoic Ctenostomata have been thought to be founded upon the creep- 

 ing bases of the zoarium and not upon the zooecium itself. The pos- 

 sible exception was in the case of Rliopalonaria in which it was 

 assumed that the fusiform swellings are really the zooecia instead of 

 the creeping base. The zooecia in both RJiopalonaria and Vinella 

 were probably deciduous and were developed by budding from these 

 pores. 



The chemical composition of the zoarium of the recent Ctenosto- 

 mata and of their supposed fossil representatives does not entirely 

 agree, although in each instance it differs from that of the other orders 

 of Bryozoa, In the recent Ctenostomata the zoarium is horny or 

 membraneous. The Paleozoic representatives contain more cal- 

 careous matter, although a considerable portion of their constitution 

 is corneous and shows a style of preservation quite unlike that of 

 associated bryozoans. Quite frequently these fossil forms have been 

 so changed that their substance now occurs as black and corneous, 

 or is replaced entirely by iron pyrites. 



The Ctenostomata may be briefly defined as follows: Zooecia 

 usually isolated and developed by budding from the internodes of a 

 distinct tubular stolon or stem. Orifice terminal, with an operculum 

 of setse, Zoarium horny or membranaceous. Marsupia wanting. 



1 Ulrich and Bassler, Smiths. Misc. Coll., vol. 45 (Quart, issue, vol. 1, pts. 3 and 4), 1904, pp. 256-294, pis. 

 65-68. 



