318 MOLLUSCOIDEA— BRYOZOA phylum 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 Upjier 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 by delicate hollow threads. 



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



Order 2. CYCLOSTOMATA Busk. 



(Bryozoaires centrifugines d'Orbigny p.p.) 



Zocecia very simple, cylindrical, calcareous, tubular, usually without transverse parti- 

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

 minutely porous ; apertural portion of zooscial tubes more or less 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 repro- 

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



Tlie families and genera of this order are founded almost entirely upon tlie 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 important cliaracter. 



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 " AlonticuU- 

 j3oro?c?s," are referred to the 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 has 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. Crisiidae Busk. 



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

 joints. Zowcia tuhilar, disposed in single or double series. 



Grisia Lamx. {Crisidia Johnst. ; 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. Zocecia tubular, the aperture salient, rounded, never 

 clustered. Interstitial cells wanting. Ovicells mei'c irregular inflations of the surface of 

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



