MELLITA. 319 



about 15."™' in diameter, the ambulacra! rosette lias all the features of the 

 adult (PL XII. f. 13), the grooves uniting the pores are deep, the madreporic 

 body is fully developed, the tubercles are uniformly distributed, the vent 

 closed by six plates (PL XII. f. 13), the first plate being still by far the 

 largest, — at this stage the difference in the rate of growth between the 

 ambulacral and interambulacral plates becomes quite as striking as in the 

 corresponding stages of Encope. There seems to be no ratio between 

 the number of ambulacral and interambulacral plates, as the older the speci- 

 men the greater seems to be the number of ambulacral plates in comparison 

 with the interambulacral plates; when measuring 15.°"°' to 16. mm - in diameter, 

 the young Echinarachnius has the general outline of larger specimens, and 

 except its size has, as far as I can see, no further distinguishing features. 



MELLITA. 



Mellita Klein, 1734. Nat. Disp. Ech. 



Test exceedingly flat. Ambulacral petals closed, remarkably well defined, 

 five or six elongated lunules in the prolongation of the ambulacral petals ; 

 when five are present the odd anterior ambulacral one is wanting, the pos- 

 terior lunule is situated in the interambulacral space. The ambulacral 

 grooves of the actinal surface are very ramified and undulating. Pillars, in 

 the interambulacral areas, separate the buccal from the digestive cavity. 

 The tubercles of the interambulacra of the lower side are very large, com- 

 paratively, between the ambulacral grooves, and small adjoining them. The 

 spines corresponding to the different sizes of tubercles are either long and 

 tapering or short and club-shaped, while larger flat-shaped spines surround 

 the lunules on the upper side. The spines of the upper surface of test are 

 all club-shaped, those edging the lunules more or less spathiform ; those 

 of the ambulacral furrows and its branches are curved, and those of the 

 large tubercles of the lower surface straight and elongate. Four genital 

 openings; madreporic body occupying central apical part of test. The 

 anus is at the proximal extremity of the interambulacral lunule, close to 

 the mouth ; outline of test circular, truncated posteriorly. 



