260 MOLLUSCOIDEA BRYOZOA SUB-KINGDOM v 



is distinguished from the remaining order, Phylactolaemata, Allman, by the complete 

 abortion of the foot, and by the circular arrangement of the tentacles. 



The Mesozoic and recent marine Gymnolaemata are almost universally divided into 

 the three sub-orders proposed by Busk, the Cyclostomata, Chilostomata, and Ctenostom.ata. 

 To these Vine has added a fourth, the Cryptostomata, and* Ulrich a fifth, the Trepo- 

 stomata ; both of which serve mainly for the reception of Palaeozoic forms. 



The detailed classification of the Mesozoic and recent Bryozoa, especially of the 

 Chilostomata, is less settled than that of the ancient types. This non-conformity is 

 due in part to the widely different views prevailing among authors as to the relative 

 value of the various characters upon which the groups are founded ; and partly 

 because the mode of growth, and zoarial characters in general, are much less constant, 

 and, therefore, less reliable than is the case among Palaeozoic representatives of the 

 class. 



Order 1. GYMNOLAEMATA. Allman. 

 Sub-Order A. CYCLOSTOMATA. Busk. 



(Bryozoaires centrifugine's, d'Orbigny, p.p.) 



Zocecia very simple, calcareous, tubular, usually without transverse partitions; the 

 orifices plain, inoperculate, not contracted, occasionally expanded; walls thin, minutely 

 porous ; apertural portion of t zocecial tubes more or lees raised, bent outwards, free or in 

 bundles ; the interspaces with or without solid or .tubular strengthening deposits. Marsupia 

 and appendicular organs wanting. .Ocecium a large cell set apart for reproductive functions, 

 or a mere inflation of the zoarial surface. 



The families and genera of this sub-order are founded almost entirely upon the form of the 

 zoarium, and the arrangement of the zooecia. The presence or absence of interstitial or 

 accessory cells and vesicular tissue (all strengthening deposits) is also an important character. 



Until quite recently it was customary to regard all Palaeozoic Bryozoans as Gydostomata, but 

 the labours of Ulrich and Vine have clearly demonstrated the fallacy of such an assumption. 

 The families Ceramoporidae and Fistuliporidae are somewhat doubtfully referred to this sub- 

 order, because they agree with its most typical members in having amalgamated and minutely 

 porous walls. Moreover, the latest investigations of Ulrich have shown that the Ceramoporidae, 

 which were clearly the progenitors of the Fistuliporidae, were in turn derived from an as yet 

 undescribed group of Chazy Bryozoans greatly resembling Berenicea and Apsendesea. 



Family 1. Crisiidae. Busk. 



Zoaria dendroid, attached by radical tubes and composed of segments united by corneous 

 joints. Zocecia tubular, disposed in single or double series. Tertiary and Recent. 



Crisia, Lam. Zoaria more or less distinctly articulated, the zocecia in a single or 

 in two alternating series. 



Family 2. Diastoporidae. Busk (emend.) 



Zoaria adnate, adhering by the entire base or only at the centre, at other times rising 

 into bifoliate leaves or hollow stems. Zooscia tubular, the aperture salient, rounded, never 

 clustered. Interstitial cells wanting. Ovicells mere irregular inflations of the surface of 

 the zoarium, ivith one or more openings. Ordovician to Recent. 



Stomatopora, Bronn (Alecto, Lam. non Leach), (Figs. 412 and 413). Zoaria delicate, 

 adnate, dichotomously branching. Zooecia sub-tubular, clavate, or elongate-ovate, 

 arranged in one or more series ; apertures sub-terminal, usually smaller than the 

 width of the cell. Ordovician, Jura, Cretaceous, Tertiary, and Recent. 



Silurian species like S. inflata, Hall, perhaps do not strictly belong to this genus. 



