SECONDARY AND TERTIARY FORMATIONS OF NORTH AMERICA. 163 



PYRIFLUSTRELLA, d'Orb. 1851. 



Colony encrusting, composed of pyriform cellules arising by a somewhat elongated 

 pedicle from the ends or sides of preceding cellules, never in contact laterally. Open- 

 ing large, and, in living specimens, closed by a membranous operculum. Behind the 

 opening we always find a special pore. 



This genus differs from Pyripora by the presence of the special pore, and from 

 Hippoihoa both by this character and by the large aperture, closed in the living state 

 by a membrane. 



P. tuberculum, d'Orb. Pal. Fr., vol. 5, p. 570. 



Hippoihoa id., Lonsd. Quart. Jour. Geol. Soc, vol. 1, p. 527. 



Pyripora id., d'Orb. Prod. Pal. Strat., vol. 2, p. 396, No. 11G7. 



" Cells pear-shaped, variously arranged ; connecting tubuli generally short or wanting rarely long ; mem- 

 branous aperture large, oval; solid surface of walls smooth, convex ; a minute tubercle near proximal ex- 

 tremity of aperture. " (Lonsd. ) 



The large aperture removes this species undoubtedly from the genus Hippoihoa, but 

 from Lonsdale's description it seems that the mark below the mouth, in his illustra- 

 tion, is a tubercle. We follow d'Orbigny in placing it in the present genus, thinking 

 it much more probable that the " tubercle " may prove to be a tubulate pore. We 

 have unfortunately never seen the species and cannot consequently decide. 



Lonsdale mentions, in some observations on the species, that in some cases he has 

 observed the membrane has been " partially or wholly obliterated " evidently mean- 

 ing, by a deposition of calcareous matter, some of the cellules in his figure being thus 

 represented. The shape of the cellule is very similar to our Pyripora irregularis, but 

 it differs in the pedicle at the proximal extremity of the cellule being much more ro- 

 bust. 



Ord. II. POLYZOA GENTRIFUGINATA. 



Cellules arising behind the preceding ones and below their mouth. 



Subord. I. C. radicellata. 

 Colony attached by corneous rootlets to sub-marine bodies. Not represented. 



Subord. II. C. agglutinata. 



Colony attached to sub-marine bodies by the same testaceous substance as that of 

 the colony or polypidom. No articulations. Colony always in one solid piece. 



Div. I. C. OPERCULATA. 



Cellules closed by an operculum. 



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