POLYZOA OR BRYOZOA. 419 



The following table exhibits the leading groups of the 

 Polyzoa : 



TABLE OF THE DIVISIONS OF THE POLYZOA. 

 ORDER I. PHYLACTOLJEMATA. 



Tentacles arranged in the shape of a horse-shoe or crescent. Mouth 

 furnished with a valve-like organ or " epistome." 



Sub-order 1. Lophopea (fresh - water). Arms of the tentacular disc 

 (" lophophore ") free or obsolete ; consistence, horny or sub-calcareous. 



Sub-order 2. Pedicellinea (marine). Arms of the tentacular disc united 

 at their extremities ; consistence, soft and fleshy. 



Sub-order 3. Rhabdopleurea (marine). Coencecium branched, adherent, 

 membranous, with a chitinous rod on its adherent side. Tentacular disc 

 horse-shoe-shaped. No epistome (?). 



ORDER II. GYMNOL^MATA. 



Tentacles arranged in the form of a more or less complete circle. No 

 valve-like organ, or " epistome," arching over the mouth. 



Sub-order 4. Paludicellea (fresh-water). Polypide completely retrac- 

 tile ; evagination of tentacular sheath imperfect ; consistence, horny or 

 sub-calcareous. 



Sub-order 5. Cheilostomata (marine). Polypide completely retractile ; 

 evagination perfect ; orifice of cell sub-terminal, of less diameter than 

 the cell, and usually closed with a movable lip or shutter, sometimes by 

 a contractile sphincter; cells not tubular; consistence, calcareous, horny, 

 or fleshy. 



Sub-order 6. Cyclostomata (marine). Cell tubular ; orifice terminal, of 

 the same diameter as the cell, without any movable apparatus for its 

 closure ; consistence, calcareous. 



Sub-order 7. Ctenostomata (marine). Orifice of the cell terminal, fur- 

 nished with a usually setose fringe for its closure ; cells distinct, arising 

 from a common tube ; consistence, horny or carnose. 



Of the above sub-orders of the Polyzoa, only the marine 

 groups of the Cheilostomata and Cyclostomata are known to 

 occur in the fossil condition ; their preservation being due to 

 their marine habits and their general possession of a calca- 

 reous or sub-calcareous ccencecium. The general facts as to 

 the distribution of the Polyzoa in past time have been already 

 alluded to. The Oldhamia of the Cambrian rocks and the 

 Graptolites have been referred to the Polyzoa; but the former 

 is probably a plant, and the latter almost certainly belong 

 to the Hydrozoa. The genus Dictyonema of the Upper 

 Cambrian, Silurian, and Devonian (fig. 52), is, however, very 



