SUB- GENUS HETEROTRYPA. 149 



Monticulipora (Heterotrypa) Trentonensis, Nicholson. 

 (Fig. 28.) 



Spec. Char. — Corallum dendroid, of small dichotomously 

 dividing branches, which are cylindrical in shape, and have a 

 diameter of from one to three lines. The surface is smooth, 

 without monticules, and destitute of clearly recognisable groups 

 of either large or small corallites. Some specimens, however, 

 seem to show faintly marked groups of tubes slightly larger 

 than the average. The calices are polygonal, about i-QOth 

 inch in average diameter, having sharp-edged angular lips, 

 surrounded internally by a depressed oval or circular ring, 

 which bounds the actual aperture of the visceral chamber. 

 The corallites are nearly vertical in the centre of the branches, 

 with thin walls and of polygonal shape, and they only turn out- 

 wards in the extreme termination of their course, so that the 

 axial region of the corallum is unusually large as compared 

 with the peripheral. In the latter part of their course, where 

 they bend outwards, they are much thickened by an internal 

 deposit of laminated sclerenchyma, but the true walls are never 

 obliterated. In this part of their course they also have a vari- 

 able but never very large number of small corallites intercalated 

 amongst those of average size. In the axis of the branches 

 the corallites seem to be destitute of tabulse ; but numerous 

 complete, horizontal, or slightly bent tabulae are developed in 

 the outer portion of the tubes, and especially at the point where 

 they begin to bend outwards. 



Obs. — The largest example of this species that I possess is 

 about two inches in length, with a diameter of about two lines, 

 dividing dichotomously at intervals of six to nine lines. Tan- 

 gential sections (fig. 28, c and d) show that the majority of the 

 tubes are from i-goth to i-iooth inch in diameter, and have 

 intercalated amongst them a variable number of smaller tubes, 

 which have a diameter of i-i5oth inch or less. In all the 

 tubes the primitive polygonal walls are thoroughly recognis- 



