OF THE l\Mll.\ OF NAIADF.S. 431 



same as cardinal tooth : posterior cicatrices distinct, the smaller 

 one being placed immediately over the large one, and against 

 the lateral tooth: anterior cicatrices distinct; dorsal cica- 

 trices situated on the under part of the cardinal tooth, very 

 perceptible; cavity of the beaks small; oacre flesh-red, vary- 

 ing from this to nearly white: iridescent in the posterior mar- 

 gin. 



Remarks. — This is variety a of U. ellipsis, described in a 

 former paper, and approaches it closely. Having seen seve- 

 ral specimens since that description was made, my doubts 

 have been satisfied, and I now consider it a new species. It 

 differs from the ellipsis in having the furrow, in being gene- 

 rally covered with fine hair-like rays, and in being always 

 more or less flesh-red inside. I have two specimens of this 

 species which present a singular format ion of the posterior 

 basal margin, which i^ dentate, the points interlocking and 

 almost hooked. The elevation anterior to the furrow com- 

 mences to swell one-third of the distance from the margin 

 to the beaks, increases as it approaches the margin, and as- 

 sumes this dentation, which being successive as the shell 

 increases ('-play- laminae of these dentations in the epider- 

 mic. In the interior tin- part of the shell has the appearance 

 of having been gouged out. It is exceedingly curious, being 

 the only specimen offiuviatile shells I have seen with a mar- 

 gin approaching to a dentate appearance. 



5. Unio I'i.sm i.\ 1 1 s. Plate l\. liii. 13 



b' 



Testa inaquilaterali, ovato-ettipticA, tranaverad ; complanatd per urn 

 boms a natibua usqvu ad marginem inferioretn, maculia quadrotia radi 

 atimpictd} natibua prominulia ; denti cardinali parvo, laterah nm 



crasso, curvato ; margarit/l aub-caruleo-albd. 



Shell inequilateral, ovate-elliptical, transverse. Battened across th< 

 umbones from the beaks to the basal margin, marked with square spots in 



form of rays; valves thick ; 1" aks slightly prominent : cardinal tooth 

 small; lateral tooth lar^c, thick and curved ; nacre bluish white. 

 VOL. III. 5 B 



