7o 



Cincinnati Society of Natural History. 



Remarks. — This species is generally regarded as the type of the 

 whole genus Monticulipora inasmuch as it was the first species described 

 by D'Orbigny. There has been considerable discussion as to what 

 was intended by D'Orbigny because there are several species similar 

 externally but differing in other ways. Dr. Nicholson admits that 

 D'Orbigny might have had in mind either this species, his M. molcsta, 

 or M. daiusoni. The selection is, therefore, somewhat arbitrary. Mr. 

 Ulrich contends that Nicholson is mistaken in his form and that M. 

 molesta is really M. mammulata D'Orb., while M. mammulata of Nicholson 

 is something else. We have followed Dr. Nicholson in selecting the 

 form known as mammulata. It is one of the commonest species of 

 the genus at many exposures of the group in Ohio and Indiana. In 

 the collection of the late Mr. U. P. James is a massive specimen about 

 nine inches in its longer and five inches in its shorter diameter. About 

 half of the longer diameter forms a dome-shaped mass, the surface 

 irregular and covered with small, closely set monticules. Inside are 

 several branches extending downward and spreading out into a won- 

 derfully interlaced mass of frondescent branches. These branches 

 are surrounded by a mass of clay. 



45. — M. pavonia D'Orb. (sp.), 1850. 



Corallum forming a thin, undulating expansion, often of con- 

 siderable extent, varying in thickness from one to about two lines, the 

 corallites in two layers with their bases fixed to a medium plane 

 marked by a delicate membrane and opening on opposite sides of the 

 corallum ; surface with low, rounded monticules, often obscure, and 

 arranged in diagonal rows at intervals of from one to one and a half lines 

 apart, occupied by calices of ordinary size : corallites generally 

 oblique at their origin, but almost immediately bending outwards, and 

 opening at right angles to the surface or nearly so ; calices elongated, 

 pentagonal, tolerably uniform in size and often arranged in obliquely 

 intersecting lines ; no interstitial cells ; walls of corallites at first thin, 

 but rapidly becoming thickened ; a few complete and horizontal 

 tabulae in some but not all of the corallites, and these often placed at 

 corresponding levels in contiguous tubes. (Prodr. de Paleont., vol. i, 

 1850, p. 22, as Ptilodictya pavonia.) (Cyc/opora jamest Prout, Trans. 

 St. Louis Acad. Nat. Sci., vol. 1, i860, p. 578; Chcetetes clathratulus 

 (James) Nicholson, Quart. Jour. Geol. Soc. London, vol. 30, 1874, 



P- 259-) 



