i84 CORALS 



important character in the determination of corals, it is so 

 in this case, because the two genera with which Sporadotrema 

 cylmdricmn is most hkely to be confused never exceed a 

 quarter of an inch in height. 



It may have been thouglit at one time that Sporadotrcvia 

 cylindriciim was only a robust and overgrown variety of 

 Polytrema, but there is no foundation for this belief. The 

 two genera are quite distinct. Apart from important differ- 

 ences of detail in the structure of full-grown examples of the 

 two genera which it is not necessary to describe in this place, 

 the young immature stages are as distinct as the adults. A 

 young Sporadotrema growing on the same support as a 

 larger specimen of Polytrema exhibits 

 all the important characters of its genus 

 and could not be mistaken for a young 

 specimen of either of the other two 

 genera. 



Sporadotrema mesenterictim (Fig. 92) 

 appears to have a much more restricted 

 range than that of S. cylindriciim, hav- 

 ing been found only in shallow water in 

 Fig. gz.spomdutrcma Torres Straits. 



mesentericum homTovv^s jj^^ ^^^^ ^f ^j^-g gpecics is character- 



straits. X 2 diams. _ _ ^ 



istic, as it consists of a number of more 

 or less erect sinuous laminae arising from a spreading 

 encrusting base. The margin is thick and crenate. The 

 laminae are sometimes interlaced so as to form a kind of 

 labyrinth of laminae, but in the simple condition of a single 

 lamina the form has a rough resemblance to a cock's comb. 

 In full-grown specimens the laminae are 15-20 mm. in 

 length, from 7 to 8 mm. in height, and from 1-5 to 2 mm. 

 in thickness. 



All the known specimens are of a salmon-red colour. As 

 regards the surface characters and general structure the 

 species does not differ in any material respects from 5. 

 cylindricum, and it clearly belongs to the same genus. 



Gypsina. — The genus Gypsina (Fig. 93) is a Foraminifer 

 which, like many others, sometimes becomes attached to 

 some rock or shell and forms encrusting discs or laminae ; 



