296 THE VEARLY FEESH-WATER MUSSELS— SIMPSOX. vol.xviii 



Swaiuson in 1840 ' divided the Unionidse into five subfamilies, from 

 a study of the shell : First, TTnioninie ( TJnio, Lamarck ; jEglia^ Swaiu- 

 son; Mt/sca, Turton); Second, HyrianiC {Iridea, Swaiuson; CastaMa, 

 Lamarck; Byria, Lamarck; Hyridella, Swaiuson); Third, hidiuime 

 (//■/>/;»«, Lamarck; CalHscapha, Swaiuson; 3Iycetopus, A. d''Orhiguy); 

 Fourth, Auodoutm^e (subgenera Anodon, Lamarck, etc.); Fifth, Alas- 

 modontinai {Alasmodo)i. Say). 



Gray in 1847,^ following the anatomical papers of A. d'Orbiguy aud 

 other authors, proposed to form a new family, Mutelidic, with the 

 genera Muiela, Leila ^ Pleiodon, and a part of Pcuyodon of Schumacher. 

 These genera differ from Unio by the presence of two distinct siphons, 

 aud were separated from the Unionid;e for that reason. Previously 

 Gray, in 1842,-' had made a family Mycetopodidte for the genus 31yce- 

 topoda, d'Orbiguy, on account of the foot presenting a remarkable con- 

 formation. 



The views of Gray have been adopted by many authors, who have 

 admitted among the Naiades of Lamarck two or three families ; others 

 an equal number of subfamilies. Thus H. aud A. Adams ^ admit two 

 families: Uniouidje (subfamilies Unioninae and Mycetopinee) and Mute- 

 lidie. Chenu^ enumerates three subfamilies: Uniouinie, Mycetopiuie, 

 and Iridinne; Gill,*^ three families: Unionidte, Iridiuidie, aud Mycetopo- 

 dida^; Clessin," two subfamilies, to which he gave the names generally 

 adopted for the families — Uniouida? and Mutelida?; Tryon,^ three fami- 

 lies: Unionida^, Iridinidic, and Mycetopodid*; and Fischer,^ two sub- 

 families: Unioninte and Mutelime. 



We see, then, that all the authors agree to make two grand divisions 

 among the Naiades of Lamarck, based upon the fact of the siphons 

 being more or less complete. The other organs of the animals, which 

 to a lesser extent serve for i)urposes of classification, liave been exam- 

 ined by Troschel'" and characterize the nine genera which are known 

 in the family Unionida?. The anatomical classification of Agassiz^' is 

 not applicable to these moUusks in North America. Isaac Lea'- at- 

 tempted to classify the Unionidae by the external characters of the shell, 

 the hinge (dorsal border symphynote or non-symphynote), the sculp- 

 ture and the form. This classification is, of course, largely artificial, 



'Treatise ou Malacology, p. 377, 1840. 



sProc. Zool. Soc. London, p. 197, 1847. 



•■'Syu. Brit. Mas., pp. 81, 92, 1842. 



-•The Genera of Recent Mollusks, II, p. 505, 1857. 



'^Manuel Conchyl. et Paleont. Couch., II, pp. 136, 147, 1862. 



t^Arrang. Families of Mollusks, p. 20, 1871. 



'Malakozool. lilatt, XXII, p. 12, 1875. 



«Strnc. and Syst. Conch., Ill, p. 237, 1884. 



^Manuel de Conchyliol., p. 998. 

 10 Wit'gmann's Archiv, XII, 1847. 



"In W. Stimpson, The Shells of New England, 1851. See also Archiv fiir Naturg., 

 1852, p. 41. 



'♦ A Synopsis of the Family Unionida*, pp. xxiv, xxv, 1870, and in earlier editions. 



1 



