SUB- GENUS MONOTRYPA. 201 



form such a conspicuous feature in many of the MonticuliporcB 

 (PI. IV. hg. 2a\ 



Tangential sections (PI. IV. figs. 2b and 2c) show that the 

 walls of the corallites are, near the surface, seemingly amal- 

 gamated, though the lines of demarcation between adjacent 

 tubes still remain visible, and they are also considerably thick- 

 ened in this region. An occasional small tube may be recog- 

 nised here and there in such sections, but these are probably 

 only young tubes, and certainly do not seem to belong to any 

 special series of interstitial corallites. 



Vertical sections (PI. IV. fig. 2d) show that the corallites 

 are slightly and regularly inclined to their surface of attach- 

 ment, being at first thin-walled, but becoming thickened as 

 they grow upwards. Tabulce are either wanting, or are but 

 occasionally developed, so far as I have seen. When present, 

 they seem to be complete and approximately horizontal. 



Both in its external features and its internal structure this 

 species is so far distinct from any other form of the genus 

 known to me as to require no detailed comparison with any 

 allied type. In spite of its encrusting character and its general 

 external resemblance to the colony of a Polyzoon, I have not 

 detected in its internal structure any marked character by 

 which it could be definitely separated from the genus Monti- 

 ciLlipora. Its tabulae appear to be very sparsely developed, 

 or, possibly, to be sometimes altogether wanting in some in- 

 stances ; but it is very difficult to prepare completely satis- 

 factory vertical sections of its corallum, and this may be due 

 simply to imperfect observation. At any rate, it is not a 

 character which would of itself separate the present form from 

 MonticulipOTa, as a similar paucity of tabulae occurs in types 

 like M. irregularis, Ulrich, and M. clavacoidea, James. 



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



