BRYOZOA. 407 



the aperture is about 0.07 mm., that of the zooecial tube just 

 beneath the aperture a little less than 0.1 mm. 



Position and locality: The specimen came from the upper 

 beds of the Trenton group in Central Kentucky. 



MONTICULIPORA d'Orbigny, 1849. 



(Prod. Pol., p. 25.) 

 (For generic diagnosis see page 370.) 



The genus Monticulipom was founded by the distinguished 

 French naturalist, d'Orbigny, for the reception of four charac- 

 teristic species of the Lower Silurian rocks about Cincinnati, 

 Ohio. Of these, M. mammulata, being the first species to follow 

 the generic diagnosis, is universally regarded as the type. The 

 original descriptions are so meagre that palaeontologists are 

 compelled to rely upon Edwards and Haime's identification of 

 the species. These authors give good figures of three of the 

 species, and of the fourth (M. filiosa) a description only. As all 

 four of the species are common and marked by easily recog- 

 nized external characters, collectors have had little difficulty in 

 identifying them. 



The genus, as defined and used by me, is founded upon M. 

 mammulata and does not include any of the other species de- 

 scribed by d'Orbigny. His M. ramosa belongs to Callopora, 

 M. filiosa to Leptotrypa, or, possibly, Monotrypa; and M. fron- 

 dosa to Heterotrypa. In this restricted sense Monticulipora 

 can, of course, include only a small proportion of the large 

 number of Bryozoa that have from time to time been referred 

 to the genus. It is only another instance showing the absolute 

 necessity of clearly describing and illustrating the minute charac- 

 ters, both external and internal, of the typical species of all 

 genera. At least sixteen species are known to me having the 

 essential characters of M. mammulata. Of this number only 

 nine have been described, the remainder being new and awaiting 

 opportunities for proper publication. 



Position and locality: So far as known, the genus is first 

 met in Trenton strata, but before the close of the Lower Silurian 

 age, i. e., the deposition of the Cincinnati group, it had already 

 reached the culminating point in its development, since only a 

 single species, the M. wmchelli from the Hamilton group of 

 Michigan, is known from rocks of later date. 



