MELL1TA SEXFURIS. 321 



of the same size, hexagonal, forming twenty equal zones (PL XI f. 1), 

 earning but a single large tubercle in the centre of each plate ; seen 

 from below the surface is deeply concave (PI. XI f. 2), the mouth much 

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

 from this side the posterior interambulacral lunule as a deep pit, at one 

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

 distance from the edge of the test, as is seen in PL XI. f. 0, representing 

 the posterior lunule of a specimen somewhat older; the rotulse are already 

 well developed in specimens of this size (Pi. XI. f. :,). 



The outline in a subsequent stage becomes slightly pear-shaped (PL XI. 

 /'. .;), the plates elongate ; the lunule pierces through to the abactinal side ; 

 the rosette is still made up of radiating pores, consisting of five to six pairs 

 of pores for each poriferous zone. The ambulacral area is now slightly nar- 

 rower than the interambulacral zones, though the plates carry as yet but a 

 single primary tubercle. Seen from below (PL XI. f. 4), we find rudimen- 

 tary phyllodes made up of a few of the small pores, which eventually 

 extend in the ambulacral furrows to the edge of the test, but are now 

 restricted to a small number clustered round the mouth (PL XI. f. 4), 

 entirely similar to those of older specimens, as seen in PL XI. f. 20, though 

 restricted in extent. When the posterior lunule has become a small round 

 opening (PL XL f. 7), encroaching upon the plates of the posterior interam- 

 bulacral area, which extends as a very faint lobe beyond the outline of the 

 test, the rosette becomes slightly pentaloid. There are now from two to five 

 tubercles on each plate (PL XI. f. 7) ; the plates are quite elongate, having 

 lost their hexagonal outline ; the lower surface is flat, and on the lower side 

 (PL XI. f. s) the ambulacra have broadened very rapidly, the interambulacra 

 forming narrow bands carrying larger tubercles between the ambulacral 

 zones, showing already in a very marked manner the difference, so promi- 

 nent in older specimens, in the character of the ambulacral and interambu- 

 lacral areas of the actinal side. The edge of the test is still quite thickened 

 (PL XI f. 7), 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 interambulacral lunule increases rapidly in 

 size ; the lunule and the groove in which the anus is placed become some- 

 what separated, being simply a depression in the continuation of the lunule. 

 After the appearance of the lunules as slight pits, which develop unequally 



