﻿GLABROUS MONTIPOR^. 21 



. 2. Montipora aubtilis. (PI, XXXI. fig. 2.) 



Description. — Corallum thin, 1 '5 mm., explanate, encrusting, edges partly expanding and 

 partly drooping. A well developed epitheca follows the growing edge. 



Calicles visible as minute dark specks, ' 5 mm. in diameter, very irregularly differentiated 

 from the surrounding coenenchyma, scattered over the surface, 2 mm. and more apart. The 

 septa, six or more, are very irregular, often mere surface granules slightly lengthened radially. 

 The fossa is deep and conspicuous, rendering the calicles just visible to the naked eye. 



Coenenchyma in section a close granular reticulum throughout, forming a dense layer 

 resting on the epitheca. At the surface the granulation is very fine and delicate, looking quite 

 smooth to the naked eye. It shows a tendency (cf. M. granulosa) to form patches of coarse 

 solid reticulum at the surface without any granules. 



There is only one small encrusting specimen (with broken edges). It measures 6 by 

 3 cm., but its size is quite sufficient, in view of the extremely minute calicles, to justify its 

 being ranked as a grown stock. The specific name is suggested by the fineness of the surface 

 texture as seen by the naked eye. 



a. Providence Eeef, Mascarenes, sand' and dead' coral. H.M.S. ' Alert.' (Type.) 



3. Montipora granulosa. (PI. I. fig. 2 ; PL XXXI. fig. 3.) 



Description. — Corallum spreads as a thin sheet (1 to 2 mm. thick) over the substratum 

 which consists of dead growths of the same, here closely following the irregularities of the 

 surface, there arching freely ; on reaching the edge of the substratum the stock droops, and 

 shows no tendency to grow out freely in the horizontal plane. An epitheca follows the 

 creeping edge. 



Calicles inconspicuous, ■ 75 mm. in. diameter, the aperture differentiated from the sur- 

 rounding coenenchyma chiefly by the radial arrangement of the coarse septa which nearly 

 fill up the fossa. Irregularly scattered, some 3 mm. apart. Six well developed primaries 

 with occasional- appearance of smaller and thinner secondaries. The aperture is not sharply 

 bounded, but the septa are merely enlarged radially arranged granules such as those which 

 cover the surface of the corallum.. Here and there the calicles appear to open irregularly 

 on slight mounds of coarse reticulum.. 



The coenenchyma consists of a coarse open-meshed reticulumr which rests upon the 

 epitheca, forming in immediate contact with it a dense solid layer distinguishable from the 

 epitheca by its glassy appearance. The upper surface is covered by the slightly projecting- 

 granular ends of reticular threads. Where the stock is increasing rapidly in. thickness, the. 



