SUB-GENUS HETEROTRYPA. 151 



thickened peripheral portion of the coralHtes thus extending 

 inwards only to a depth of about 5-iooths of an inch. This 

 fact, taken together with the circumstance that the tubes open 

 very obliquely to the surface, renders the preparation of tan- 

 gential sections very difficult. The small tubes, as seen in 

 long sections, are decidedly more closely tabulate than the 

 large ones, but appear to agree with the latter otherwise in 

 their structure. 



I originally believed (Pal. of Ontario, 1875, p. 11), from 

 a merely macroscopic examination, that this form might be 

 identified with the Monticulipora pulckella, E. and H., of the 

 British Silurian deposits. Its microscopic structure is, how- 

 ever, quite peculiar, and is so distinctive that it is unnecessary 

 to institute a detailed comparison between it and any other 

 species known to me. 



Horizon and Locality. — Abundant in the Trenton Limestone 

 of Peterboro', Ontario. (Collected by Dr George Jennings 

 Hinde, F.G.S.) 



Monticulipora (Heterotrypa) Girvanensis, Nicholson. 



(Fig. 29.) 



C/uefcifs sp., Nich. and Eth. jun., Mon. Sil. Foss. Girvan, vol. i. p. 43, I'l. 

 III. figs. 2-2b, 1878. 



Spec. Char. — Corallum dendroid, of small branches which have 

 a cylindrical or sub-cylindrical shape, and are from rather more 

 than a line to three lines in diameter. Surface devoid of tuber- 

 cles or of groups of either large or small corallites, but showing 

 the oval or circular, slightly prominent calices of the larger 

 tubes, sometimes with the apertures of the smaller tubes be- 

 tween them. Corallites of two kinds, large and small. The 

 large corallites have a diameter of about i-yoth inch on an 

 average, and each is surrounded, in the outer part of its course, 

 by a well-developed and thickened wall, their form being oval 

 or circular, and the points at which they come in contact being 

 thus very limited. There is, also, no actual or apparent amal- 



