XIV SYNOPSIS OF 



Mr. Gray, in his excellent List of Genera (Zool. Soc. Proceedings, 1847), divides the 

 Naiades into three families, viz. : — 



Family 9th. Unionid^;. 10th. Mutelad^e. 11th. Mycetopodid^e. 



The Unionidee consists of eight genera, viz. : Anodonta, Cuv. ; Margaritana, Schum. ; Monocondyloea, 

 D'Orb. ; Unio, Retzius; Barbala, Humph.; Lamproscapha, Swain.; Anodonta, Lam.; Byssodonta, D'Orb. 



Family 10th. Mutelad^! consists of five genera, viz.: Mutela, Scopoli; Leila, Gray; Pleiodon, 1 

 Con.; Paxyodon, Schum.; Prysodon, Schum. 



Family 11th. Mycetopodid^; consists of one genus, viz.: Mycetopus, D'Orb. 



M. D'Orbigny, in his Voyage Am. Merid., vol. v. p. 594, (1835 to 1843,) divides the 

 family into genera according to the form of the mantle, the form of the foot, and according 

 to the character of the shell. 



"Qui se divisent zoologiquement en plusieurs genres d'apres la forme du manteau, la forme du pied, 

 et d'apres les caracteres seuls de la coquille. On pourraits les diviser ansi qu'il suit." 



1. Manteau ferine jusqu'au tiers inferieur de la coquille, pourvue des deux tubes distincts, &c. = 

 Iridina, Lam. 



2. Manteau ferine - seulment sur la region anale, ou il y a deux tubes distincts, &c. = Castalia, Lam. 



3. Manteau ouvert sur toute sa longeur, une ouverture anale seule distincte, &c. = Mycetopus, 

 D'Orb. 



4. Manteau ouvert sur toute sa longeur une ouverture anale seule distincte. 



A. Coquille pourvue des dents variables a la charniere = Unio, Retz. 



B. Coquille pourvue cl'une seule dent = Monocondyloea, D'Orb. 



C. Coquille sans dents a la charniere = Anodonta, Lam. 



M. Troschel, in Wiegmami's Archives, vol. xiii. 1847, divides the family, by their 

 anatomical structure, into nine genera, viz. : — 



Unio (Retzius). The mouth lips are wider than long, united as far as the middle on the posterior 

 margin. The margin of the mantle entirely open; the outer branchia united to the mantle to its very 

 extremity ; the inner branchia not united to the foot ; the foot is tongue-shaped, thick, somewhat pro- 

 duced anteriorly. ( Unio tumidus, Retz, and Unio Hopetonensis, Lea.) 



Margaritana (Schumacher). (Alasmodonta, Say.) The mouth lips are wider than long, united 

 along two-thirds of the posterior margin. The mantle entirely open; the outer branchia is free poste- 

 riorly, and lies in a fold of the mantle; the interior branchia is united to the foot anteriorly, but along 

 the greater part of the foot it is free; the foot is tongue-shaped, somewhat produced anteriorly. (My a 

 margaritifera, Lin.,) Tab. 6, Fig. 1. 



Hyria (Lam.). The mouth lips as wide as long, not united. The mantle margin inferiorly is open, 

 posteriorly closed, so as to make a branchial and anal aperture. The outer branchia united to the 



1 I do not see any reason for throwing out Iridina and taking in its place the name of Pleiodon, which was 

 unnecessarily given to a shell well known and figured long before, and described both generically and specifically, 

 viz., the Iridina ovata, Swain. 



