172 



Unio cuneatuSj Var. Barnes. (^Note to Hildreth's essay.) 

 Unio planulatus, Lea. Trans. American Philos. Soc. N. aS'., 

 vol. 3, pi. 9, ^. 13. 



Desc. Shell transversely oblongovate, thick ; surface yellowish 

 .brown, with several rather broad radii, which are often interrupted, 

 by the larger lines of growth, into spots ; disks and umbo com- 

 pressed ; beaks simple or not undulated ; not elevated ; cavity of 

 the hinge membranes or lunule oval, acute ; ligament not elevated; 

 within white, somewhat grooved obtusely ; cardinal plate very 

 thick, with a considerable flattened space between the cardinal 

 and lateral teeth ; cardinal teeth rather small, direct ; lateral teeth 

 very short, oblique, and veiy thick ; anterior smaller muscular 

 impression immediately anterior to the tips of the lateral teeth. 



Ohs. A striking similarity exists between this shell and the 

 cuneatus and gihhosus of Barnes, the latter of which, however, is 

 somewhat more slender, the cardinal teeth larger, the lateral teeth 

 longer, the beaks undulated. 



In a note on Dr. Hildreth's description of phaseolus, Barnes 

 says it is a " white variety of cuneatus ;" and it must be confessed 

 that a considerable resemblance exists between some of their varie- 

 ties. But the latter species differs in the much less dilated car- 

 dinal plate ; in having the anterior smaller muscular impression, 

 situated immediately beneath the tip of the lamelliform teeth ; in 

 having the anterior lunule much more depressed, with slightly 

 elevated lines crossing the wrinkles. 



The young of a corresponding age, accurately resembles, in its 

 outline, Barnes' figure of his mucronatus, but his description of 

 mucronatus agrees better with cuneatus than with any other species, 

 certainly much better than with gihhosus, inasmuch as it is stated 

 to be " purplish on the margin, and whitish in the centre," whereas 

 the latter is more commonly whitish on the margin than in the 

 centre, and the " anterior lunule long, distinct, with a marginal 

 furrow," of mucronatus, agrees with cuneatus, but not at all with 

 gihhosus. 



This species is found in plenty in the Wabash, and is probably 

 also an inhabitant of most of the larger tributaries of the Ohio. 



The branchial oviducts, when inflated with eggs, exhibit a series 

 of tubes, which, when dried, appear granulated under the micro- 

 scope ; these tubes are dirty yellowish, with a few blackish spots 



