318 MOLLUSCOIDEA— BRYOZOA phylüm v 



or stolons arranged radially ; surface with a single row of pores. Ordovician to 

 Lower Carboniferous. 



Heteronema Ulr. and B, (Fig. 437, F). Zoaria as in Vinella but threads are with- 

 out radial arrangement. Ordovician to Upper Carboniferous, 



Allonema Ulr. and B. (Fig. 437, A). Zoaria composed of distinct, minutely 

 punctate vesicles or connected internodes. Silurian to Lower Carboniferous. 



? Ptychocladia Ulr. and B. Upper Carboniferous. 



Family 3. Ascodictyonidae Ulrich. 



Zoaria parasitic, of pyriform porous vesicles arranged in radial Clusters, or isolated 

 and connected hy delicate hollow threads. 



Ascodictyon Nich. and Etil. (Fig. 437, D, E). Silurian to Lower Carboniferous. 



Order 2. CYCLOSTOMATA Busk. 



{Bryozoaires centrifugine's d'Orbigny p.p.) 



Zocecia very simple, cylin^rical, calcareous, tubulär, usually without transverse parti- 

 tions ; the orifices piain, inoperculate, not contracted, occasionally expanded ; walls thin, 

 minutely porous; apertural portion- of zooecial tuhes more or less raised, hent outwards, 

 free or in bundles ; the interspaces with or without solid or tubulär strengthening deposits. 

 Marsupia and appendicular organs wanting. Ocecium a large cell set apart for repro- 

 ductive functions, or a mere inßation of the zoarial surface. 



The families and genera of tliis order are founded almost entirely upon the form of the 

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

 accessory cells and vesicular tissue (all strengthening deposits) is also an iiiiportant character, 



For many years it was customary to regard all Paleozoic Bryozoans as Cyclostomata, but 

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

 The families Ceramoporidae and Fistuliporidae, often regarded as Trepostomata or ^'Ifonticuli- 

 poroids," aivereferred tothe Cyclostomata because they agree with its most typical members in 

 having amalgamated and minutely porous walls. In 1890 Ulrich discovered ovicells in certain 

 genera of the Fistuliporidae, while more recently Bassler lias shown the occurrence of the 

 same structures in the more primitive Ceramoporidae. 



Suborder A. TUBULIPORINA Hagenow. (Tubulata Gregory). 



Zocecia monomorphic, of elongated, cylindrical tubes grouped into bundles, sheets or 

 linear series. The Tubuliporina comprise the typical Cyclostomata and in all probability 

 give rise to the other suborders. 



Family 1. Orisiidae Busk. 



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

 joints. Zocecia tubulär, disposed in single or double series. 



Grisia Lamx. {Grisidia Jolinst. ; Filicrisia d'Orb.). Zoaria more or less distinctly 

 articulated, the zooecia in a single or in two alternating series. Cretaceous to Recent. 

 ? Unicrisia d'Orb. Cretaceous. 



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. Zooecia tubulär, the aperture salient, rounded, never 

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

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



