122 
TEEPOSTOMATA. 
Order TEEPOSTOMATA, Ulrich, 1882. 
[E. 0. Ulrich, American Palaeozoic Bryozoa : Journ. Cincinnati Soc. Nat. Hist. 
vol. V. p. 151.] 
Diagnosis. 
Bryozoa with a zoarium composed of closely packed zooecia, 
which are prismatic or cylindrical and attached to one 
another throughout their length. The zoarium is massive 
or consists of thick laminae. The zooecia are monomorphic 
or dimorphic ; they begin as simple, thin cyclostomatoid 
tubes, all of which may develop into zooecia, or the develop- 
ment of some of them may be arrested, and these form the 
mesopores. The distal ends of the zooecia usually have 
thickened and moniliform walls. The zooecia and mesopores 
are usually attached throughout their length, but they may 
be slightly separated by interzooecial spaces. Diaphragms 
generally present. Acanthopores and cystiphragms often present. 
Aeeinities. 
The Order Trepostomata is of most importance in the Palaeozoic 
era, and the fossils belonging to it so closely resemble many of 
the tubular Alcyonarian corals that some Bryozoa may still be 
included in the Alcyonaria and vice versa. 
Cainozoic Trepostomata may usually be distinguished from 
corals by their histological structure ; but when this test cannot 
be applied, owing to the recrystallization of the fossil, it may be 
doubtful whether a specimen be an Alcyonarian or Bryozoan. 
Thus, while many authorities, including Lindstrdm and E. 0. 
Ulrich, refer the Monticuliporidae to the Bryozoa, Waagen, Wentzel, 
and Sardeson regard them as Alcyonaria ; and Mcholson represents 
them as a group allied to the .Alcyonaria but constituting an 
independent order. The arguments for their Alcyonarian affinities 
are clearly stated by Mcholson ^ and Sardeson,^ and some of the 
histological evidence seems weighty ; but in such old Palaeozoic 
fossils the skeletal material has usually undergone molecular 
rearrangement, and the radial structure sometimes present is 
probably due to secondary recrystallization. 
^ H. A. Nicholson. “ On the Structure and Affinities of the genus Monti- 
etilipora and its suhgenera,” 1881, pp. 62-78. 
“ F. AV. Sardeson. “ Ueber die Beziehungen der fossilen Tahulaten zu den 
Alcyonarien ” : Neu. Jahrh., Beil.-Bd. vol. x. pp. 347-50. 
