116 PROCEEDINGS OF THE ACADEMY OF [1888. 



margin bluntly rounded, basal margin witli a tendency to emargina- 

 tion in old females; quite uniformly curved in males; greatest 

 diameter near the middle of the ligament, greatest length at posteri- 

 or end of dorsal line; cardinal teeth double in both valves, compress- 

 ed, very oblique, crenulate, the anterior tooth in the right valve is 

 much the smaller, as is the posterior one of the left valve; lateral 

 teeth single in the right and double in the left valve, curved and 

 slender; nacre light purple and spoted with a few dark-waxy spots; 

 •dorsal cicatrices two to four and in a diagonal row from the base of 

 the anterior cardinal tooth across the centre of the cavity of the 

 beak, anterior cicatrices distinct and well impressed. 



Diameter .8. Length 1.2. Breadth 2i inches. 



Habitat. Lake Ashby, Volusia County, Florida. 



Museum Acad. Nat. Sci. Phila. Newcoml) Coll., Cornell Univ. 

 Nat. Museum. 



Remarks. This delicate species, is possibly related to U. jjapyra- 

 cem Gould. But Dr. Gould in his description of that species, says 

 that "it resembles Anodonta Coujoeriana Lea, in shape, delicacy and 

 even color." 



But there is nothing in U. Averellii to remind one of An. Coiqjeri- 

 ana Lea. It has the outline of U. occitltus Lea, but its affinity is 

 with U. rutilans Lea, but differs in being very thin, almost paper- 

 like, less blunt at each end, and without a depressed area at the 

 anterior ligament. Named for Mr. Wm. D. Averell publisher of 

 the Conchologist's Exchange, of Philadelphia, Pa. 



Unio Nolani. Plate IV, fig. 1. 



Shell wide, smooth, rather thick, beautifully polished throughout, 

 and entirely covered with heavy greenish rays; epidermis yellowish 

 and often olivaceous ; dorsal margin arcuate, anterior margin grace- 

 fully and perfectly rounded, l)asal margin subemarginate, posterior 

 margin uniformly rounded from the end of the ligament to the base 

 with no tendency to biaugulation; umbonial angle flatly rounded; 

 umbonial slope flattened, depressed in the middle; beaks small, 

 pointed, undulated, and rather prominent; cavity of the shell small ; 

 cardinal teeth heavy, erect, grooved, double in the left and single in 

 the right valve ; lateral teeth curved, heavy and much roughened ; 

 nacre beautiful pink and iridescent. 

 Diameter .9 Length 1.5. Breadth 3 inches. 



Mus. Acad. Nat. Sciences. My own cabinet. 



Habitat: A creek flowing into St. John's River, near Palatka, Fla. 



