70 CORALS 



Mitva polonica, or Polish cap, on account of its cup or cap 

 shape. 



Although many variations in its exact form are now- 

 known, the most characteristic specimens are deeply concave 

 on the under surface, the area round the central fossa being 

 raised on the top of the convex upper surface. The numerous 

 septa passing radially from the fossa to the circumference 

 of the coral are not all straight and continuous, as the\' are 

 in Fungia, but some of them appear to be deeply indented 

 in their course, forming pit-like depressions to which neigh- 

 bouring septa are inclined and from which new septa arise. 



These pits represent the position of a series of small 

 secondary polyps arranged more or less irregularly in a ring 

 or series of rings round the central polyp of the fossa. 



Herpetolitha 1 is the next genus in this series, and can 

 usually be distinguished from the other genera by its elon- 

 gated form, which is sometimes bent in a serpentine fashion 

 (Fig. 25). Running along the middle of the upper surface 

 is a long deep fossular groove in which the septa appear 

 to radiate not from one centre but from a number of distinct 

 centres, and the septa on each side of the groove are inter- 

 rupted in the same manner as they are in Halomitra by a 

 large number of irregularly scattered pits. 



In a figure of a living Herpetolitha given many years 

 ago by Dana it is shown that in the flesh that covers the 

 median groove there is a series of mouths, each one sur- 

 rounded by a patch of bright green colour in marked contrast 

 to the brown colour of the tentacles and other parts of the 

 coral polyp, and similarly that in each of the lateral pits 

 there is a little mouth surrounded by a green patch and a 

 circle of browm tentacles. We have in Herpetolitha, there- 

 fore, an advance on the structure of Halomitra in that the 

 corallum is constructed by a number of larger polyps in the 

 median fossa and a greater number of smaller polyps 

 situated laterally. 



Specimens of this genus sometimes reach a very con- 

 siderable size. There is a specimen in the Manchester 

 Museum 13 inches in length and 3^ inches in width, which 



1 Frequently spelt Herpolitha by authors. 



