﻿GLABROUS HONTIPOR^. 23 



' 5. Montipora explanata. (PI. I. fig. 3 ; PL XXXL fig. 5.> 

 Montipora explanata, Briiggemann, Phil. Trans., clxxiii. (1879) p. 577. 



Description. — Corallum explanate, 7 to 8 mm. thick, smooth, with wavy surface ; growing 

 edge 2 mm. thick, not supported by epitheca, which is developed only in patches. The stout 

 corallum grows over former growths, spreading evenly from elevation to elevation, leaving 

 large free spaces underneath. 



Calicles crowded, from about one diameter apart ; aperture • 75 mm. Septa irregular 

 and feebly developed, except one primary which is often prominent and: exsert. On the 

 under surface, the calicles are numerous, irregularly distributed, the smallest being minute 

 pinholes without septa, only here and there the single large primary faintly indicated. 



Coenenchyma, in section, shows the typical streaming reticular layer which passes ventrally 

 into a very dense, often quite solid layer pierced by the ventral polyp cavities, and dorsally 

 into a closely knit thickening layer, often sharply marked off from the horizontal layer. The 

 vertical elements of this bent up layer are here and there almost as regular as trabeculae, but 

 they are not thickened or otherwise differentiated, and the layer is truly a reticulum. On 

 the surface, the level interstitial spaces consist of a very coarse granular reticulum. 



The type specimen was first briefly described by Briiggemann in an account of new 

 coral species from the Eed Sea and from Mauritius.*" He did not name it, however, as he 

 was not certain whether it might not be the Maiiopora lichen of Dana. As there can be no 

 question about the total absence of anything like " subtubiform protuberant calicles " such as 

 are described by Dana for his M. lichen, Briiggemann, in working out the corals from Piodriguez, 

 dismissed this suggested relationship and united it with two others from that locality under a 

 new name " explanata." 



Briiggemann further compared this specimen with Dana's M. scahricula. The two may 

 agree in general appearance, but the vertical threads of the thickening layer show more 

 tendency in the latter coral to rise up as minute tubercles above the surface of the ccenen- 

 chyma ; and further, from Dana's drawing of a section of that type,t these vertical elements 

 form stout trabeculse at considerable distances from one another — a condition in marked 

 contrast to that shown by a section of M. explanata. 



The two specimens from Rodriguez, classed with this coral by Briiggemann as a and h, 

 also have the vertical elements of the thickening layer differentiated into stout trabeculse and 

 are thus placed elsewhere (cf. M. perforata and 3f. venosa). 



The single type specimen is much distorted on the upper surface by commensal Balanids. 



a. Mauritius. (Type.) 



*Abh. Nat. Ver. Bremen v. (1878) p. 399. f Cf. Zoophytes, pi. xlvi. fig. 3c. 



