MARGARITA. 285 



Genus MARGARITA Leach, 1819. 



Margarita LEACH, Thomson's Annals of Philosophy, xiv, p. 202 

 (1819) ; Appendix to Capt. Ross's Voyage, H. M. S. Isabella and 

 Alexander, p. 59. BRODERIP and SOTVERBY, Zool. Journ., iv, p. 

 363. SOWERBY, Mai. and Conch., Mag. i, p. 24; and of authors 

 generally (not Margarita Leach, Zool. Misc., i, p. 107, 1815,= 

 Avicula}. Margarites Leach MS. 1819, GRAY, Ann. and Mag. N. 

 H. xx, p. 268 (1847). Eumargarita FISCHER, Manuel de Conchy 1., 

 p. 825 (1885). Valvatdla GRAY, Guide Syst. dist. Moll. Brit. Mus., 

 p. 157, 1857 (type M. grcenlandica=undulata Sby.). 



" In 1814, Leach used the name Margarita for a section of A vicula 

 which had already received several names. The name Margarita 

 was therefore a synonym. In 1819, he used the same name, this 

 time for a valid genus ; but apparently recognizing that this might 

 cause confusion, he changed the termination in a work which he 

 had in press in 1820, and which was interrupted by his death. 

 .This work was published some thirty years later by Dr. J. E. Gray. 



" The second use of a generic name once fallen into synonymy, 

 although not forbidden by the accepted rules for nomenclature, is 

 greatly to be deprecated ; yet when it has occurred and when the 

 second application of the name is universally unchallenged for 

 more than half a century, and the original application never was 

 in use and has been absolutely ignored, I can see no benefit likely 

 to accrue to science from a change of names." 



The history of the name Margarita, briefly given in the above 

 extract from Dr. Dall's Report on ' Blake Gastropoda,' justifies us, 

 in my opinion, in retaining that name for the present group. 



The species of Margarita, like all boreal shells, are excessively 

 plastic and variable. Many of them are circumpolar in distribu- 

 tion. They were first monographed by the elder Sowerby in 1828, 

 and figured in the ' Conchological Illustrations.' Philippi included 

 the species in his monograph of Trochus in Kiister's Chemnitz, but 

 he recognizes many forms which have no real specific characters. 

 Mr. G. B. Sowerby, Jr., monographed the group in Reeves' Iconica, 

 vol. 20. He confuses true Margarita with Photinula, Solariella and 

 Minolta; and the work, on account of the numerous and egregious 

 blunders it contains, is worthless. 



M. HELICIXA Fabricius. PI. 64, figs. 45, 46, 47 ; pi. 39, fig. 63. 



Shell umbilicate, thin, depressed-conoidal, flesh-colored, with 

 paler at periphery and below the suture, fading into corneous around 



