76 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Mellita. 



Agasmz, 1841. Mon. Scut., p. 34. 

 Type, Scutella quinquefora Lamarck, 1816. Anim. sans Vert., 3, p. 9 = Echinodiscus quinquesperforatus 



Leske, 1778. Add. ad Klein, p. 133. 



Like the preceding this is strictly an American genus but whereas two thirds 

 of the species of Encope occur on the west coast of tropical America, two of the 

 four species of Mellita occur on the east coast. These clypeastroids gi ve every 

 indication of high specialization, not only in the extreme flatness of the test with 

 the accompanying peculiarities of lantern and auricles, but in the lunules, the 

 position of the periproct and even in the spines and pedicellariae. The spines 

 are solid and the primaries are more or less swollen at the tip (PL 125, figs. 17, 

 18); they may be somewhat curved, while many of the miliaries are abruptly 

 bent (PL 125, fig. 16). The pedicellariae are greatly reduced in size and number 

 and no ophicephalous are to be found. All have but two valves and these are 

 of peculiar shape. Calcareous particles in the pedicels seem to be nearly or 

 quite wanting; sometimes a few small rods may be present. The lunules afford 

 the best characters for separating the species, both the number and the size and 

 form being of real importance. There are four species which seem to be valid. 



Key to the Species of Mellita. 



Lunules 5. 



Interambulacral lunule very variable in length but usually less than 30 

 length, and seldom much longer than posterior ambulacra! lunules; if unus- 

 ually long its breadth will be .15-.20 of its length qirinquiesperfo 



[nterambulacral lunule long and very narrow, from .25 to .40 test-length and 

 40-100% longer than posterior ambulacral lunules: its breadth is less than 



.10 length longijv&a. 



Lunules 6. 



[nterambulacral lunule long and narrow, its length at leasl twice and usually 

 several times its own breadth sextet 



Interambulacral lunule broad and rounded, its length only about 25* [ more 



than its breadth jwrifica. 



Mellita quinquiesperforata. 



Echinodiscus quinquiesperforatus Leske, 1778. \dd. ad. Klein, p. 133 



Mellita quinquiesperforata Meissner, 1904. Bronn's Thier-reichs, 2. abi. 3, buch 4, p. 



Plate 125. figs. t6-21. 



Pedicellariae are very scarce but the bidentate at Least are quite character- 

 istic. The valves are only .12-.1S mm. in Length; they are somewhat compressed 



