American Palaeozoic Bryozoa. 



131 



t}^pes of Monticulipora which occur in the Cincinnati Group of Ohio, 

 all of which are more or less identical in external characters, and any 

 one -of which might, therefore, be supposed to be the genuine JI. mam- 

 mulata, of D'Orbign} T , and of Milne-Edwards and Haime. These three 

 or four types are the following : 



"(a). The form which I have here described as M. mammulata, which 

 grows in thin undulated fronds, and has its surface covered with mon- 

 ticules, which are sometimes low and rounded, sometimes conical, some- 

 times elongated." 



The form which I have spoken of above as probably a variety 

 of the preceding, which it resembles generally in its microscopical 

 characters, except that it has a much smaller number of interstitial 

 corallites. In its mode of growth it is massive, and its monticules are 

 pronounced and conical or elongated."" 



(JI. Jilasa, D'Orb. I would suggest that Dr. Nicholson again 

 examine this form, when I think he will find that the interstitial cells 

 are not only much less numerous, but that, in reality, true interstitial 

 tubes are entirely wanting). 



"(c). The form which I shall describe subsequently, under the name 

 of M. molesta, and which reliable investigators regard as the true JI. 

 mammulata. This form is most commonly frondescent, and has the 

 form of a thin undulated lamina, but it is occasionally massive; its 

 surface is covered 'with well marked conical monticules, which are 

 sometimes elongated, and its microscopical structure is entirely dif- 

 ferent to that of the two preceding types." 



tl (d). A form which has a frondescent corallum, and a surface cov- 

 ered with prominent elongated monticules, but which has an entirely 

 peculiar microscopic structure, unlike that of any of the forms previ- 

 ously mentioned. This will be subsequently described under the name 

 of JI. dawsoni, Nich." 



Of these four species, D'Orbign}-, without any doubt, had three be- 

 fore him when he described the genus, i. e. types a, b and c. M. daw- 

 soni, Nicholson (type d), should fall from this list of possible type 

 species, for it is a rare species, and does not appear to occur at Cin- 

 cinnati, and, consequently, the probabilities are strong that the species 

 was not in the possession of D'Orbigny. Nicholson goes on to state: 

 "As before remarked, any one of the above, so far as its external 

 features go, might very well stand for JI. mammulata, D'Orb.: and in 

 attempting to decide to which of these this title really belongs, we do 

 not get much help from the descriptions given either by D'Orbigu}-, or 



