148 



THE GENUS MONTICULIPORA. 



been justified, perhaps, in treating- of it at all in this place ; and 

 my only apology for giving even the above short description of 

 its characters is, that it possesses a structural feature which I 

 should have felt unwilling to have passed over without notice. 

 It illustrates, namely, in a remarkable manner, those peculiar 

 structures which occur in so many of the Montimliporcu and 



StenoporcE, and which I have 

 termed " spiniform corallites." 

 Thus, if we examine a tangen- 

 tial section (fig, 27), we observe 

 at the angles of junction of the 

 normal corallites, or between the 

 thick walls of two adjoining 

 tubes, a number of clear circular 

 spaces of comparatively large size 

 (from i-500th to i -450th inch 



Fig. 27.— Tangential section of a few coral- in diameter). Some of these 

 lites of Monticulipora implicata, Ulrich, i , i 



enlarged fifty times, shoeing the large!- ^Icar spaccs preserve the Same 



and smaller ordinaiy tubes, and the character thrOUghout, but mOSt 



peculiar "spiniform corallites." 



of them exhibit centrally either 

 a dark spot or small clear ring. These spaces are, therefore, 

 clearly sections of tubes, and there can be no doubt that the 

 spines which stud the thick walls of the calices (PI, II. fig, 7^) 

 are the upper terminations of these same tubes. I have not 

 succeeded in detecting any opening at the apices of these 

 spines, though their tubular nature would lead one to expect 

 that such must exist, I have, however, I think, succeeded in 

 satisfying myself that their cavities, as seen in long sections, 

 are crossed by distinct horizontal tabtilce. This is a point of 

 importance, as tending to confirm my view that these hollow 

 spines, in this and in the many other cases in which they occur, 

 are really of the nature of very peculiarly modified and special- 

 ised corallites. 



Horizon and Locality. — Cincinnati Group, Ohio. 



