MontlculiporaO BRYOZOA. 217 



The principal and almost infalliable distinguishing peculiarity of the family is 

 the cystiphragm. As a rule th*ese structures form continuous series in the zooecial 

 tubes, and in all such cases their nature is at once determinable in either vertical 

 or tangential thin sections. But in the genera Monticulipora and Mesotrypa they are 

 often modified so that they might be mistaken for simple, oblique or slightly curved 

 diaphragms. On plate XV figures 8 and 9 illustrate the latter, while of the usual 

 form of the cystiphragms many examples are figured on plates XV to XIX. 



Genu3 MONTICULIPORA, d'Orbigny. 



• Monticulipora, d'OKBiGNY, 1850. Prodr. de Paleont., t. i, p.,25. 

 Monticulipora (part.), Nicholson, 1879. Struct, and Affln. of the Pal. Tabulate Corals, p. 269. 

 Peronopora (Tpa.Tt.), Nicholson, 1881. "The Genus Monticulipora," p. 215. 



Monticulipora,Vi,TiiCB, 1882, Jour. Gin. Soc. Nat. Hist., vol. v, pp. 153 and 232; 1890, Geol. Surv. 111., 



vol. vili, pp. 370 and 407. 



Zoarium massive, lobate, subramose, laminar, incrusting, or frondescent. Sur- 

 face usually tuberculate'd, sometimes even. Monticules closely arranged, usually 

 conical, often elongated or compressed. Zooecia polygonal, generally rather small, 

 with thin and, internally, peculiarly granulose walls, ilesopores few, generally 

 absent entirely. Cystiphragms present in the zocecial tubes, both in the axial and 

 peripheral regions of the zoarium, usually in continuous series, but often isolated. 

 Acanthopores small, more or less numerous. 



Type : M. mammulata d'Orbigny. 



As now restricted this genus embraces but a small part of the incongruous ma- 

 terial for which the genus was a receptacle from the day it was established. Still, 

 no less than eighteen species having the essential characters of M. mammulata, all 

 of them Lower Silurian save one, are known to me. The earliest of these is from 

 the Birdseye limestone, and several belong to the Trenton proper ; but it is in the 

 Hudson River rocks that the genus has its strongest development. So far the genus 

 is not known in Upper Silurian deposits, and it is possible that all its species became 

 extinct at the close of the Lower Silurian. If that should prove to be true the M. 

 winchelli Ulrich, described from the Hamilton of Michigan, could not be retained as 

 a true member of the genus, since its line of development would necessarily be 

 different. 



