72 MADREPORAKIA. 



57. Porites Florida 2. (P. Floridm sccunda.) (PI. III. fig. 8.) 

 [Florida Eeefs, coll. Agassiz and Thomson ; British Museum.] 

 Syn. P. clavaria Pourtales (non Lamarck), Mem. Mus. Comp. Zool. vii. i. (1880), pi. xii. figs. 4, 5, 6. 



Description. — The corallum divides into cylindrical stems about every 3 cm., and at rather 

 small angles. The branches tend to bend up into the vertical, and, though smooth, show signs of 

 slight swellings at points where they failed to fork, apparently from want of space. The tips 

 are round and blunt, from 1 to 1 • 5 cm. tliick, and consist of a streaming laminate reticulum, 

 out of which calicles are being differentiated. The living layer extends 3 • 5 to 4 cm. down the 

 cluster, which is short, stout, and squat, but showing graceful curvings into the vertical. 



The calicles are about 1'5 mm. in diameter, conspicuous and not deep. The walls 

 appear at their edges to consist of a smooth glistening thread, very thin and running in an 

 irregular zigzag, giving off short septal processes at the angles. This is the condition near and 

 below the tips, but lower down the branches, just below the edges of the wall, the skeletal 

 elements thicken so suddenly as to make it appear as if the thread-like edge rested upon a 

 shelf, from the inner edges of which the stout septa rose up to the level of the thread. In 

 such calicles which become more and more pronounced, the wall-thread is more or less 

 polygonal, and runs clear of a ring of radial septal plates. The inner edges and tips of the 

 septa, quite smooth near the tips of the branches, are finely echinulate in the more adult 

 portions and frequently swollen. Five pali, round-topped and conspicuous, rise up in the 

 middle, sometimes connected with septa. In the centre is the columellar tubercle, which rises 

 to the height of the pali. To these pali and central tubercles, other small irregular granules 

 may now and then be added outside the ring of pali, but without visible connection either 

 with septa or paU ; all these obscure the fossa. 



This specimen is that represented by the figures referred to above in the synonymy. It is 

 remarkable for the change in the character of the calicles, which is very striking, even to the 

 naked eye. Those on the upper portions have the ragged openly-reticular appearances, 

 characteristic of so many of the West Indian forms, wliile down below there is a precision not 

 often met with, and which the artist in the original figure, No. 5, attempted to bring out. 

 But inasmuch as the specimen was not sufficiently cleaned of animal matter, he did not 

 succeed in giving the exact details. The thin edge standing upon the suddenly thickening 

 wall — sometimes joined to the septa, sometimes free from the septa, sometimes even wanting 

 between two rows of exsert, radial, septal plates — has so far not been recorded for West Indian 

 forms. The new figures here given bring out the differences in the calicles. 



The slightly fusiform shape of the branches has been already noted, see p. 59 ; wliile the 

 sudden thickening of the elements just below the surface is seen again in P. Florida 5 and in 

 P. Bermuda 1 (see p. 143). 



a. Presented by Sir John Murray. Zool. Dept. 91. 2. 3. 19. 



