SUB GENUS HETEROTRYPA. 131 



characters, but also by numerous more or less important fea- 

 tures in their internal structure. 



I have ventured to name this species in honour of the late 

 Professor E. B. Andrews, who is well known to geologists by 

 his published labours in connection with the geological survey 

 of Ohio. 



Horizon and Locality. — Cincinnati Group, Cincinnati, Ohio. 



Monticulipora (Heterotrypa) Ulrichii, Nicholson. 



(Fig. 22.) 



ChcBtetes ELic/ien', Nicholson, Quart. Journ. Geol. Soc, vol. xxx. p. 504, PL 

 XXIX. figs. 6-6a, 1S74. Pal. Ohio, vol. ii. p. 197, PL XXI. figs, y-y^z, 

 1875. Ann. Nat. Hist., sen 4, vol. xviii. p. 90, PL V. fig. 14, 1876. 



Spec. Char. — Corallum ramose, of cylindrical or sub-cylin- 

 drical branches, which divide dichotomously at irregular inter- 

 vals, and vary in diameter from less than two lines to about 

 four lines. The surface is smooth and destitute of monticules, 

 but in well-preserved specimens minutely spinose ; the calices 

 sub-polygonal or rounded, mostly from i-iooth to i.-90th inch 

 in diameter. Interspersed with the openings of the ordinary 

 corallites are the minute irregularly rounded apertures of a 

 largely developed series of small interstitial corallites. 



As regards internal structure, the corallites are at first thin- 

 walled, but become thickened in the outer part of their course, 

 their walls becoming at the same time seemingly fused together. 

 The small angular interstitial corallites occupy all the intervals 

 left between the oval or rounded large tubes, and there is a 

 largely developed series of thick-walled hollow tubuli (" spini- 

 form corallites"), placed at the angles of junction of the normal 

 corallites. Tabulae are wanting, or are very sparingly devel- 

 oped in the axial region of the branches, but are abundantly 

 present in the outer portion of the tubes, and are much more 

 closely set in the small interstitial corallites than in the large 

 ones. In all cases, the tabuLx are complete and approximately 

 horizontal. 



