92 



CORALS 



As the general form of the colony of Madrepora is so 

 variable, it affords no characters by which the genus can be 

 safely distinguished from others. A close examination of 

 one of the terminal branches is necessary to find characters 



to be relied upon for this 

 purpose, and fortunately 

 these characters are so 

 definite that it is nearly 

 always quite an easy 

 matter to determine for 

 certain whether a given 

 coral is or is not a member 

 of the genus Madrepora. 



Each terminal branch 

 bears at its extremity a 

 single large apical cah'x, 

 and below this a number 

 of oblique calices of 

 smaller size, arranged like 

 a series of brackets on all 

 sides of the branch. The 

 smallest of these brackets 

 are next to the apical 

 calyx, the largest ones 

 farthest away from it (Fig. 

 j8). In some varieties 

 the apical calyx is thick- 

 walled and dome-shaped, 

 so that the terminal 

 branches are blunt or 

 knob - like. The lateral 

 calices have in these 

 varieties more definitely 

 the appearance of being arranged in a radial manner round 

 a very thick-walled axial calyx. Such varieties are some- 

 times regarded as belonging to the sub-generic groups Isopora 

 and Tylopora. More rarely the axial calices are more or 

 less laterally compressed and the lateral calices arranged 

 principally in two series (sub-genus Distichoc^'athus). 



Fig. 38. — ^Madrepora. .-\. tcrniinal branch 

 of a large colony of a Stag's-horn variety. 

 ;■: 2 diams. 



