loS THE GENUS MONTICULIPORA. 



can judge from an examination of thin sections of this single 

 specimen, I am disposed to regard it as a mere variety of the 

 present species. 



Before leaving this form, It Is necessary to inquire briefly 

 what erounds there are for reo-arding; it as the M. inamiindata 

 of D'Orbigny ; and on this point, I regret to say, there is but 

 little that can lead in the meanwhile to any positive conclu- 

 sions. Good observers, indeed, are of opinion that the pres- 

 ent form is really the ]\I. frondosa of D'Orbigny, and that 

 the form which I shall describe afterwards under the name of 

 M. niolcsta is the true J/, maimnnlata ; and though I myself 

 decidedly differ from this view of the subject, I not only can- 

 not pretend to establish my owm view beyond controversy, 

 but I am oblifjed to admit that there exists much o-round for 

 a legitimate difference of opinion on this point. The diffi- 

 culties which environ this question arise from the fact that 

 there are at least three, possibly four, distinct structural types 

 of Moiiticulipora 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 AI. viainnuilata of D'Orbigny, and of Milne- Edwards 

 and Haime. These three or four types are the following : — 



{a) The form which I have here described as J/, maninui- 

 lata, which grows in thin undulated fronds, and has its sur- 

 face covered with monticules, which are sometimes low and 

 rounded, sometimes conical, sometimes elongated. 



{b) 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. 



(<f) The form which I shall describe subsequently under the 

 name oi M. moles fa, and which reliable investigators regard as 

 the true M. mauimulata. This form is most commonly frondes- 

 cent, and has the form of a thin undulated lamina, but it Is 



