196 



liave induced many, and myself amongst the number, to consider 

 this shell as the young of gihhosus, Barnes ; but a very slight ex- 

 amination serves to show that it is very distinct. The young of 

 that species is always much more elongated transversely, not so 

 thick, with the beaks much undulated, and the series of small 

 cicatrices in the cavity of the beaks is jjarallel to the hinge mar- 

 gin. As respects magnitude it approaches parvus, Barnes, which, 

 however, has the beaks undulated, is rather thin, with oblique, 

 small, cardinal teeth. Plate 41. 



Unio CAMPTODON. — Specific character. Beaks distinct from 

 the posterior margin ; lamelliform teeth arquated at tip. 



Desc. Shell moderately thin, transversely oblong-oval, a little 

 compressed, dark brownish, or blackish ; beaks with regular small 

 undulations, behind the middle but remote from the posterior edge, 

 but little prominent; ligament slope somewhat compressed, with 

 two distinct compressed lines ; umbonial slope not elevated above 

 the level of the disk ; anterior margin a little prominent towards 

 the base and rounded ; lunule large ; posterior margin prominent, 

 extending far behind the beaks and rounded ; base a little con- 

 tracted in the middle ; within milk white ; teeth, a single rather 

 long, oblique, undivided primary tooth in each valve ; lateral teeth 

 rather slender, towards the tip a little arquated. 



Ohs. This interesting, new shell was sent to me by Mr. Bara- 

 bino, who discovered it opposite to New Orleans in ponds. An 

 exterior view of the shell would not immediately distinguish it 

 from Alasmodonta edentula, nob., but the inner surface is quite 

 different, and the armature of teeth separates them generically. 

 PI. 42. 



Unio lugubris. — Desc. Shell transversely subovate, inflated, 

 dark brownish, wrinkled ; umbones prominent ; beaks not ver}- 

 prominent, eroded ; ligament margin slightly arquated ; ligament 

 more or less concealed ; anterior margin very widely rounded, 

 sometimes truncate or even subemarginate ; posterior margin rather 

 prominent, but very short ; base often a little contracted in the 

 middle ; within pale lilac ; cardinal teeth oblique, compressed, 

 denticulated ; lamelliform teeth slightly arquated, granulated and 

 striated at tip ; posterior accessory cicatrix rounded, rather deep ; 

 anterior margin somewhat iridescent. 



