460 ox A NEW SrECIES OF DIASERIS, 



The genus is tlius described: — " Biasen's. Corallum simple, 

 free, discoid, witli a bare and costulate wall with, a structure 

 similar to Cijeloseris, but in its young state it is formed of a 

 certain number of separate petaliform lobes wliicli in tlie more 

 mature state become more or less united by their edges." The 

 authors add that in all the various families of corals no other 

 instance of this structure is known. Two species were described 

 by them, Diaseris distorta, Michelin, of unknown habitat and D. 

 Freyclneti. Both were large, viz., 50 millimetres across and 10 

 high, and the differences between the species were that D. 

 Freycineti was a coral with closer septa which were not so high 

 as D. distorta. See Hist. Nat. des Corallaires, Yol. III., p. 54. 

 Also Comptes Eendus de I'Academie des Sc, Yol. XXIX., 1849, 

 p. 72. 



The species to which I have now to call attention is very much 

 smaller than either of the preceding and there are also peculiarities 

 in the septa as I shall proceed to show. 



Diaseris Mortoxi, n. s., Plate XY., fig. 1,2. 

 Corallum semicircular, thin, subdiscoid, divided into two, three 

 or four lobes in some specimens, though the majority are 

 completely semicircular with an entire rounded edge. Base flat 

 or concave in the slightest degree, showing no trace of any former 

 separation between the lobes. Costa distinct, fine, granular and 

 corresponding with the septa, but all equal in thickness and 

 taking their origin from the edge at distances the same at the 

 various orders ; the outer edge of the septa projecting like the 

 teeth of a fine cog-wheel outside the base. In nearly all the 

 specimens these were four distinct systems, though some had 

 only three, two, and some with only one and the rudiments of two 

 others. The cycles depended on the age of the specimens. They 

 ranged from five to eight incomplete. All are granular, but the 

 granules are in ridges so as to give rise to a vermicular surface 

 and the ridges project at exactly opposite sides of the septa; the 



