MONTICULIPORIDJE. 



355 



trypella, Dia?iulites, Dip/otrypa, Defray ia, Ste/iopora, &c, and ranges 

 from the Ordovician to the Permian period. 



The type of the genus Monticulipora is the M. mammulata, D'Orb., 

 of the Ordovician rocks of North America, which Mr Ulrich identifies 

 with the form described by the writer under the name of Peronopoi'a 

 molesta. In this form, the corallum (fig. 224, a) has usually the shape of 

 a laminar erect expansion, composed of two layers of tubes which open on 

 the two sides of the frond. The large tubes or " autopores " are placed 

 close together, and just before reaching the surface their walls become 



a ^^S^Xe v 





Fig. 230. — Morphology of Montictdipora mammulata, D'Orb. { = Peronopora molesta, Nich.), 

 Ordovician, Cincinnati, a, Tangential section taken immediately below the surface, enlarged 

 twenty times, b, Tangential section taken at a greater depth below the surface, similarly en- 

 larged, c, Vertical section, showing one side of the double frond, similarly enlarged, d, e, and 

 F, Portions of the preceding sections enlarged forty times : a, Autopores ; ;;/, Mesopores ; ac, 

 Acanthopores ; ta, One of the " cystoid " tabulae of an autopore, the rest of the tube being crossed 

 by straight tabulae. (Original.) 



considerably thickened ; hence there is a considerable difference between 

 sections taken just below the actual surface (fig. 230, A and d) and those 

 taken at a little depth (fig. 230, B and e). Interstitial tubes or mesopores 

 are developed in small number, and are easily recognised in long sections 

 by their close tabulation (fig. 230, f). Acanthopores are developed in 

 great numbers, and form a ring round each autopore (fig. 230, d), but 

 they are difficult to recognise except in tangential sections taken close to 

 the surface. The autopores are furnished with two sets of tabulae, each 

 tube showing a series of vesicular or " cystoid " tabulae on one side (fig. 

 230, F, ta) with a series of straight tabulae in the other half of the tube. 

 Owing to this peculiarity in the tabulation of the autopores, tangential 

 sections (fig. 230, b) exhibit the cut edges of the cystoid tabulae in the 



