I90 THE GENUS MONTI CU LI FOR A. 



but I do not think that this is more than a mere result of im- 

 perfect calcification, and I have not detected any " spiniform 

 corallites." Small interstitial tubes are also entirely wanting. 



Longitudinal sections (fig. 39, b) show the duplex character 

 of the wall quite as conspicuously as do tangential slices. 

 They show, also, that there is no difference in the tabulation of 

 the tubes of the clusters as compared with those which con- 

 stitute the bulk of the colony. All alike are furnished with 

 remote and complete tabulae, which are approximately hori- 

 zontal, and which continue to be developed till close upon the 

 surface. 



Monticitlipora piilchella, E. and H., is sufficiently distin- 

 guished from all other species of the genus known to me, 

 both by its marked superficial characters and its exceptionally 

 simple internal structure. The form which I formerly de- 

 scribed under the name of Chcetctes pulchcllus, from the Cincin- 

 nati Group of Ohio, proves on microscopic examination to be 

 entirely distinct, and has been previously described under the 

 name of M. Andrewsii. 



Horizon and Z,^^^///)'.— Wenlock Limestone, Dudley. So 

 far as my limited experience goes, the species is a very rare 

 one. 



Monticulipora (Monotrypa) petasiformis, Nicholson. 

 (Fig. 40.) 



Spec. CJiar. — Corallum small, discoidal, from six to eighteen 

 lines in diameter, somewhat variable in shape, but always with 

 a flat or concave base, which may be in part attached parasit- 

 ically to some foreign body, but is always covered with a con- 

 centrically striated epitheca over the rest of its extent. From 

 this basal plate the short corallites spring nearly at right angles 

 throughout, and they either form a thin disc, or they give rise, 

 more commonly, to an expansion which is thin at its edges, 

 but is prominently elevated towards its centre, thus resembling 

 in form the " cap " of many kinds of mushrooms, hi other 



