THE FAMILY OF NAIADES. XV 



mantle to its extremity ; the interior branchia is united to the foot ; the foot tongue-shaped, thick, some- 

 what produced anteriorly. (JT. symatophora, Lam.,) Tab. 6, Fig. 3. 



Castalia (Lam.). The mouth lips a little wider than long. The margin of the mantle inferiorly 

 is open, posteriorly so united that the branchial and anal apertures are closed; the branchial aperture 

 is surrounded with cirri; the anal aperture smooth; the outer branchia united to the mantle all the way 

 to its extremity; the inner branchia (?); the foot tongue-shaped, thick, somewhat produced ante- 

 riorly. D'Orbigny, Voy., &c. [Castalia ambigua, Lam.) 



Dipsas (Leach). Animal unknown. Shell closed entirely [Dipsas plicatus, Leach). 



Anodonta (Lam.). The mouth lips are broader than long, united to the middle of the posterior 

 margin ; the mantle margin is entirely open ; the outer branchia united to the mantle to its extremity ; 

 the inner branchia not united to the foot; the foot is thick, tongue-shaped, somewhat produced anteriorly. 

 [An. cygnea, Lam.) 



Iridina (Lam.). Mouth lips longer than wide, not united; mantle margin united as far as the foot, 

 so that the branchial and anal apertures are closed; the outer branchia united to the mantle as far as its 

 extremity; the inner branchia entirely united to the foot; foot thick, tongue-shaped, somewhat produced 

 anteriorly. (/. cselestis, Lea.) 



Spatha (Lea). The mouth lips are longer than wide, and not united. The mantle margin is closed 

 behind, so that the bronchial and anal apertures are closed ; on the under margin the mantle is entirely 

 open; the outer branchia is united to the mantle all the way to its extremity; the inner is not united to 

 the foot; the foot is thick, tongue-shaped, somewhat produced anteriorly. [S. rubens, Lea,) Tab. 6, Fig. 2. 



Mycetopus (D'Orbigny). The mouth lips longer than wide ; the mantle margin is open to the anal 



aperture, which is closed ; the outer branchia is entirely united, or grown together ; the inner (?) ; 



the foot is very much produced and widened into a knob. [M. soleniformis, D'Orb.) 



In The Shells of New England, by W. Stimpson, Boston, he states that, in the MSS. 

 of Prof. Agassiz, the following divisions into genera are made (of the New England species) 

 on anatomical differences, viz. : — 



Unio, Retzius, emend. Gills free from the abdominal sac, their posterior extremity attached to 

 the mantle; eggs, in the female, filling the whole extent of the outer gill; mantle fringed at both 

 siphonal openings. (Agassiz, MSS.) [Unio eomplanatus, Lea.) 



Eurynea, Rafinesque, emend. Gills attached to the abdominal sac, leaving no communication 

 between the pedal and the upper gill cavities; eggs received in the sacs of the posterior part of the outer 

 gill; mantle fringed at the posterior half of its ventral edge, and at the branchial and anal siphons. 

 ( Unio preelongus, Bar.) 



Lampsilis, Raf., emend. Gills attached; eggs in the posterior part of the outer gill; mantle 

 fringed at both siphonal openings, and having fleshy thickenings and processes at its posterior ventral 

 edge. (Unio radiatus, Lam.) 



