SUB- GENUS MONOTRYPA. 185 



of small interstitial tubes. Vertical sections (fig. 37, d and e) 

 show that there is no difference whatever in structure between 

 any one set of corallites and any other. In none are the walls 

 thickened towards the surface, but they are uniformly thin 

 throughout, and are often slightly wavy. The course of the 

 tubes is straight, there being no curvature near their bases, 

 and they increase in number in passing outwards by the inter- 

 polation of fresh tubes. In a great number of the tubes no 

 tabulae exist at all ; but an occasional tabula is sometimes de- 

 veloped near the mouth of the tube, or at some depth below 

 the surface. 



In internal structure, M. clavacoidea, James, is most nearly 

 allied to M. irregularis, Ulrich ; but the form of the corallum 

 and the mode of growth afford a sufficient means of separation. 



Horizon and Locality .—Q.\\\(:\\\W2X\ Group, Cincinnati, Ohio. 

 (Coll. U. P. James.) 



Monticulipora (Monotrypa) calceola. Miller and Dyer. 



(PI. I. figs, z-y.) 



Alonticulipora calceola, Miller and Dyer, Journ. Cincinnati Soc. Nat. Hist., 

 vol. i. 1878. 



Spec. Char. — Corallum free (?), of small size, varying from 

 less than one line up to more than six lines in diameter, 

 helicoid in shape, and traversed by a horn - shaped cavity, 

 which opens upon the exterior by a well-marked circular aper- 

 ture, the inner lining of which shows encircling striae, and which 

 varies from half a line or less up to more than two lines in 

 diameter. Surface smooth, or covered with low rounded tuber- 

 osities. Calices approximately equal, thin-walled, and poly- 

 gonal in shape. Corallites radiating from the outer surface of 

 the afore-mentioned central tube to open in a nearly rectilinear 

 manner upon all points of the surface except the external aper- 

 ture of the central tube. Corallites polygonal, thin-walled, 

 from I -90th to I -70th inch in diameter, very minute angular or 



