PROCEEDINGS OF THE UNITED STATES NATIONAL MUSEUM 



issued W4-V\A^ VJ^MS h the 



SMITHSONIAN INSTITUTION 

 U. S. NATIONAL MUSEUM 



Vol. 89 W..hington: 1940 No. 3099 



A REVISION OF THE KEYHOLE URCHINS (MELLITA) 



By HuBEET Lyman Clark 



Several months ago my good friend Austin Hobart Clark, of tlie 

 United States National Museum, called my attention to a series of 

 Mellitas in the national collectio]i that offered some problems in 

 identification. He kindl}^ asked me to make a critical study of the 

 material and subsequently sent it to Cambridge. For this favor I am 

 sincerely grateful and offer Mr. Clark my hearty thanks. 



Supplementing this most interesting lot with the large series of 

 specimens in the Museum of Comparative Zoology has enabled me 

 to segregate some new forms and to reach some conclusions as to 

 the composition of the genus that are apparently nearer the truth 

 than those hitherto generally held. 



In 1921 Lambert and Thiery in their "Essai de Nomenclature 

 Raisonnee des Echinides" (fasc. 5, p. 32-1) revived the name Leodia 

 (Gray, 1851) for the species of Mellita having six lunules. In view 

 of the facts that a fifth lunule is present in ambulacrum III and 

 that the ambulacral lunules do not originate as in Mellita quinquies- 

 perforafa by the closing up of marginal notches but by resorption of 

 the test through orally developing pits, this action is amply justified. 



Leodia is apparently monotypic so far as Recent species are con- 

 cerned, with sexies'perforata Leske of the "West Indian region as the 

 only valid species. There is an upper Miocene species, caroliniana 

 (Ravenel), that is apparently distinct from sexles perforata^ but the 

 Recent species erythrea Gray and pacl-flca Verrill are of dubious 

 validity. Gray's species is based on specimens of sexiesperforata 



240599—40 435 



