288 BULLETIN OF THE 



Young specimens of Mellita hexapora, measuring ^ of an inch in di- 

 ameter, are almost circular, with a thickened raised edge, as in Laganum, 

 and a-; yet have no lunules. The rosette is simply a series of radiating 

 pores, three and two in each poriferous zone, for each ambulacrum, ex- 

 tending but a short distance from the apex. The ambulacra! and inter- 

 ambulacral plates are of the same size, hexagonal, forming twenty equal 

 zones, carrying but a single large tubercle in the centre of each plate ; 

 8een from below the surface is deeply concave, the mouth much larger in 

 proportion to the test than in adult specimens, and we see forming from 

 this side the posterior intcrambulacral lunule as a deep pit, at one ex- 

 tremity of which is placed the anus near the mouth, about one third the 

 distance from the edge of the test. We find also rudimentary phyllodes 

 made up of a few of the small pores, which eventually extend in the am- 

 bulacral furrows to the edge of the test, but are now restricted to a small 

 number clustered round the mouth. The outline in a subsequent stage 

 becomes slightly pentagonal, the plates elongate; the lunule pierces 

 through to the abactinal side ; the rosette is also radiating, made up of 

 five to six pairs of pores for each poriferous zone. The ambulacral 

 area is now slightly narrower than the intcrambulacral zones. When 

 the posterior lunule has become a small round opening, encroaching 

 upon the plates of the posterior interambulacral area, extending as a 

 lobe beyond the outline of the test, the rosette is slightly petaloid. 

 There are from two to five tubercles on each plate ; they are quite 

 elongate, having lost their hexagonal outline ; the lower surface is 

 flat, and on the lower side the ambulacra have broadened very rap- 

 idly, the interambulacra forming narrow bands carrying larger tuber- 

 cles between the ambulacral zones. The edge of the test is still 

 quite thickened, and it is only when the young Mellita has attained 

 somewhat less than half an inch in diameter that the ambulacral 

 lunules appear as pits, seen at first from the lower side only, and 

 gradually forcing their way through the test. The posterior inter- 

 ambulacral lunule increases rapidly in size ; the test and the groove in 

 which (lie anus is placed become somewhat separated from it, being 

 simply a depression in the continuation of the lunule. After the ap- 

 pearance of the lunules as slight pits, which develop unequally, not ap- 

 pearing simultaneously, the changes are limited to the increase in size 

 of the lunules and of the poriferous ambulacral zone on the lower side; 

 the outline and tjcneral faciei, with the exception of the larger size of 

 the tubercles, being that of the adult. 



