130 LEA ON THE GENUS ACOST^A OF D'ORBIGNY. 



there was a single specimen in London. He says "this is one of the most singular 

 of known genera," and he considers it intermediate between Etheria and Ostrea, and 

 as apparently connecting the regular fresh water bivalves with the marine bivalves 

 and with the genus Etheria, iYiasrauch as in the sinus at the posterior extremity of 

 the ligament it resembles the Naiades and the Etheria, and in its singular muscular 

 impression, as well as its general form, it approaches to Ostrea. "The shell adheres 

 by one valve, the structure is foliaceous. It has only one muscular impression ; the 

 impression of the mantle is irregular and indistinct. The ligament is long. It has 

 a sinus like the Naiads.''' The figure Avhich represents this sinus, gives it very much 

 the form so peculiar to the South American Naiades. In the " Conchologists 

 Nomenclator," by Catlow and Reeves, the genus Mulleria is omitted, but a note is 

 inserted to say, " that it had been contested amongst naturalists that the Mulleria of 

 Mr. Sowerby (Ferussac) is nothing more than an obscure variety oi Etheria. Upon 

 lately examining this remarkable shell, in the collection of Thomas Norris, Esq., we 

 were much struck with its appearance, and it is probable that the genus may be 

 adopted in a future number of the " Conchologia Iconica.'^ 



M. Deshayes in his new and able work, " Traite Elementaire de Conchyliologie," 

 constitutes his 20th Family on the single genus Etheria, and places this Family 

 after that of Mytilacea and before Rudistea. It forms his 62d genus. The Mulleria 

 constitutes his 23d Family, which follows Malleacea, and is followed by Pecte?iidea. 

 It forms his 73d genus, Vulcella being the 72d and Lima the 74th genus. Thus 

 Mulleria is brought near to the beginning of his order (un pied) of the 2d sub-class 

 Monomyaria. 



In the Systematic arrangement of Mr. Gray, his Family Etheriadce is placed 

 between Chamidce and Carditidce, and he makes that family consist of Etheria and 

 Mulleria, with a question as to Mulleria being admitted. 



Latreille, in his " Regne Animal," places Etheria in his first Family oi Dimyaria, 

 but he begins his system with the more perfect organic forms. 



In the " Siemens de Zoologie " of Milne Edwards, Etheria is placed after Perna, 

 and he remarks that it has much analogy to Ostrea. He does not notice Mulleria. 

 D'Orbigny in his description of Acostcea (Mulleria?) places it in the Family 

 UnionidcB, between the genera Anodonta and Etheria. But if we admit the two grand 

 divisions of Monomyaria and Dimyaria, this position would not be tenable. Its true 

 position indeed is at the commencement of the Monomyaria. 



It appears somewhat singular, that M. D'Orbigny should not have mentioned the 

 analogy his Acostcea bears to the figure of Mulleria in all the representations made of 

 it, particularly that of Sowerby in his genera. In considering all the characters of 

 the two shells, as well in the descriptions as in the figures, the conclusion seems 

 inevitable, that if they do not form a single species, they both belong to the same 

 genus. In examining the various excellent figures given by Sowerby, it will be 



