FAMILY UNIONID.E UN 10. 



189 



Unio boydianus. 

 (state collection.) 



Unio boydianus. Lea, Trans. Am. Phil. Society, Vol. 8, p. 216, pi. 16, fig. 32. 



Description. Shell obovate, rather inflated, very inequilateral, subangulate before, with 

 regular rather close and nearly equidistant marks of growth. Substance of the shell rather 

 thin, thicker before. Beaks rather prominent, with small undulations at the tip : ligament 

 rather short and thin. Epidermis yellowish brown, striate. Cardinal teeth compressed, 

 double in both valves ; lateral teeth long and nearly straight. Anterior cicatrices distinct ; 

 posterior cicatrices confluent ; dorsal cicatrices on the under side of the cardinal tooth. Cavity 

 of the shell deep and rounded ; cavity of the beaks shallow and subangular. Nacre white 

 and iridescent. Length, 1*2. Breadth, 1-9. Diameter, 0*8. 



Such is the description by Mr. Lea of a species which is found in Oak-orchard creek, Or- 

 leans county. Dr. Boyd presented me with the same shells from that locality, and T then 

 considered them as probably a variety of U. ochraceus, Say ; to which, as Mr. Lea remarks, 

 they are most nearly allied. My specimens were all radiated more or less distinctly behind. 



Unio radiatus. 



PLATE XVin. FIG. 236. 



(STATE COLLECTION.; 



Mya radiata. Gmel. Syst. Nat. 3220. 



Unio id. Lam. An. sans vert. Vol. 2, p. 668. 



Unio radiants. Barnes, Am. Journ. Sciences, Vol. 6, p. 265. Hildbeth, Id. Vol. 14. 



Margai-Ua ( Unio) id. Lea, Am. Phil. Tr. Vol. 3, p. 415 , Vol. 6, p. 127, pi. 15, fig. 48, 49. 



U. id. Conead, Monog.pl. 10, fig. 2. Russel. Ess. Jour. Vol. 1, p. 60. 



V. id. Gould, Invertebrata of Mass, p; 110, fig. 73. 



Description. Shell varying from fragile to robust, oblong-ovate. Anterior margin narowed, 

 regularly rounded ; posterior broadest and angulated on its surface, rounded on its margin 

 Beaks near the front of the shell, slightly elevated. Hinge-margin elevated, sub-compressed. 

 Cardinal teeth erect, triangular, bifid, crenulate. 



Color. Epidermis light green or olive, with numerous darker green concentric zones, and 

 lighter colored radiations from the beaks to every part of the margin ; within bluish white, 

 occasionally very iridescent. 



Transverse diameter, 1-0 -3*0; vertical ditto, 03-1-6. 



This is also a common species, occurring everywhere through the Northern and Middle 

 States. Those communicated to me from Massachusetts, appear to be more robust and some- 

 what more elongated than those procured in this State. It may be necessary to state, that 

 many of the plates of this and the succeeding genera were drawn reversed, an error which 

 was not discovered until the impressions were all printed off : with a knowledge of this fact, 

 the reader will not be misled in studying the species. 



