158 



FlG. 46. Polygnathus 

 simplex, x 13 

 after Hinde). 



If is t ing u is h ing ( 'haracters. — Body 

 shaped like a tenter-hook, nearly oval in sec- 

 tion; hook pointed, opposite end smooth, 

 pounded like an articular surface; promi- 

 nent median ridge extending from point to 

 opposite end. 



Found in the Conodont bed of the Gene- 

 see,at Section 1 (very abundant). (Hinde.) 



Class Bryozoa. Ehrenberg. 



The Bryozoa, or Polyzoa, arc marine or fresh- water invertebrates, 

 almost always occurring in colonies, which increase by gemmation. 

 Each eooid of the colony is- enclosed in a membranaceous, or calcareous, 

 double-walled sac, the zocecium, into which it can withdraw. The ani- 

 mal possesses a mouth, an alimentary canal, and an anal opening, and, 

 in addition to these, a fringe of respiratory tentacles — the lophophore. 

 The colony is commonly attached to foreign bodies, which it either in- 

 crusts or from which it arises as an independent frond. 



In the Paheozoic genera the cell apertures are often surrounded by 

 elevated rims, or peristomes. In many forms a portion of the posterior 

 wall of the tube is more or less thickened, and curved to a shorter radius, 

 projecting often above the plane of the aperture. This forms the lunaria, 

 and their ends may project into the tubes as pseudo-septa. In the inter- 

 apertural space may occur angular or irregular cells, the mesopores, while 

 on many portions of the surface, tubular spines (acanthopores), or nodes 

 (rounded, knob-like elevations), may occur. At intervals, in many 

 genera, rounded elevations, or monticules, are found, which may, or may 

 not, be destitute of cells. Macula or irregular blotches, destitute of 

 cells, also occur in many forms. Many species bear a superficial resem- 

 blance to certain corals, particularly the Monticuliporoids. 



Note.— The anatomy of recent Bryozoa (Polyzoa) may be found in the 

 text-books of zoology. An admirable and comprehensive discussion of the 

 structural features of living Bryozoa will be found in the introduction 

 to Simpson's "Hand-book of North American Palaeozoic Bryozoa," pub- 

 lished in the 14th Annual Report of the State Geologist of New York, 

 1894. In the '•Hand-book" itself, the Palaeozoic genera are described 

 and illustrated. Ulrich's systematic description of the Bryozoa. in 

 Zittel's Text book of Palaeontology (Eastman's translation), will he found 

 of great value, and also his "Palaeozic Bryozoa." (Geol. Surv. 111., Vol. 

 VIII., 1890.) 



