SECONDARY AND TERTIARY FORMATIONS OP NORTH AMERICA. 159 



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The poverty of this unpretending little species, in distinctive characters has sug- 

 gested the name we propose for it. The very thin annular walls, simply rounded, 

 without any markings, at 'times crowded, at other times distinctly spaced, but always 

 distinctly separated, will distinguish it. 



We have observed one colony, in which each cellule was provided with its ovarian 

 vesicle, and in another, we could not find a trace of even a broken one. What Ave 

 call abortive cellules above, may prove to be vibracular openings, though we cannot 

 make out any distinct arrangement ; they are sometimes numerous and close together 

 at Other times entirely absent. 



M. sexpunctata, n. s., fig. 44. — Colony encrusting, composed of large elliptical to 

 irregularly pyriform cellules, placed irregularly, in contact and often crowding each 

 other. Aperture of the same shape as the cellule and occupying nearly its whole sur- 

 face. Walls convex, slightly constricted about the aperture, overhanging the interior ; 

 marked by a variable number, but usually six pits or depressions, occasionally sur- 

 rounded by a minute rim. Ovarian vesicles small, overlapping the succeeding cellule, 

 surface unknown. 



From the American tertiary ; either Eocene or Miocene ; probably the latter ; 

 locality unknown. 



We have seen two colonies, or probably parts of the same colony encrusting an un- 

 determined, many-layered species of a Polyzoon ; to which is also attached the only 

 specimen, we have seen, of our species Reptoflustrella tuoulata. It is in the Museum 

 of the Academy of Natural Sciences, Philadelphia. 



M. speciosa, G. and H., fig. 45. 



Membranipora speciosa, G. and H., Proceedings Acad. Nat. Sci., 1860, p. 567. 



Colony encrusting in irregular patches, composed of elongated, oval cells, often 

 crowded out of their normal shape. Cells arranged in longitudinal lines and in some- 

 what irregular quincunx, often assuming a transverse arrangement ; aperture occupy- 

 ing the whole of the surface, cell walls plain, angular at their edge or slightly rounded. 

 Interior of the cell, regularly concave, with the sides of the concavity reaching almost 

 to the top of the walls ; in new cellules the germinal plate only is seen. This ger- 

 minal plate often extends for a considerable distance beyond the colony (half an inch) 

 and is marked by irregular longitudinal lines, frequently bent suddenly in an oblique 

 direction and then continued longitudinally as before. Between the cellules are 

 frequently open angular spaces, caused by the inaccurate apposition to the cellules. 



From Chiriqui, Central America, probably Miocene. Encrusting a specimen of 

 Obeliscus Evansii, Gabb. Coll. W. M. G. 



This is the only species in which we have ever seen such an enormous extension of 



the germinal plate. In this instance, its greatest length equals or exceeds the longest 



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