]94 NEW UNIONISE OF THE 



passing from the centre of the cavity of the beaks, obliquely, at the base of the 

 cardinal tooth; palleal cicatrix well impressed; cavity of the shell shallow and rather 

 wide ; cavity of the beaks shallow and subangular ; nacre silvery white and iridescent. 

 Remarks. — Two valves, — right and left, — belonging to different individuals, both 

 bleached and nearly deprived of the epidermis, were all which were received from Prof. 

 Forshey by the Smithsonian Institution some years since. I had been greatly in hopes 

 of getting better specimens from the Professor to make a description from, but he has 

 not, during the last year, been able to find others. Therefore, neither the description 

 nor figure are as perfect as could be desired. It is remarkable for its outline, which 

 will at once call to mind the form of many species of the marine genus Tellina. 

 The most striking characteristic is the form, size and place of the cardinal teeth. In 

 the left valve the tooth is very large and double, and the posterior half is the largest 

 and is placed in part posteriorly to the point of the beak. In the right valve the cardinal 

 tooth is single, more compressed and placed anteriorly to the point of the beak. The 

 peculiarity in the form of these teeth causes the plate to be diminished to a mere 

 line. The superior anterior cicatrix in one valve is distinct from the great one below, 

 in the other valve it is nearly so. I have no doubt that they will be found in most 

 specimens to be distinct. In both they are deeply impressed. It is to be greatly 

 regretted the specimens were not in a better condition. The epidermis being much 

 bleached and worn cannot be described with any degree of certainty ; but there 

 remains enough to satisfy us that it will be found in perfect specimens to be yellow- 

 ish, probably straw yellow, and it may have some rays, but these valves do not dis- 

 play any sign of them. The beak of one valve has the remains of small undulations 

 at the tip. It is nearest in outline to U. crassidens, Lam., but it resembles it in few 

 other characters. The character of the cardinal and lateral teeth are totally dif- 

 ferent. 



Unio Heermannii. PI. 26, fig. 263. 



Testa alata, lsevi, elliptica, compressa, valde intequilaterali, postice obtuse biangulata, antice rotunda ; 

 valvulis subtenuibus, antice irregulariter crassioribus ; natibus prominulis, vis undulatis ; epider- 

 mide luteo-fusca, niieanti, eradiata; dentibus cardinalibus parvis, subeonicis, crenulatis, in utroque 

 valvulo duplicibus ; lateralibus longis, laruellatis subrectisque ; margarita pallido-salmonia, purpures- 

 cente et intense iridescente. 



Shell winged, smooth, elliptical, compressed, very inequilateral, obtusely biangular 

 behind, round before ; valves rather thin, irregularly thickened before ; beaks a little 

 prominent, scarcely undulate ; epidermis yellowish brown, shining and without rays ; 

 cardinal teeth small, subcorneal, crenulate and double in both valves ; lateral teeth 

 long, lamellar and nearly straight ; nacre pale salmon and purplish, and exceedingly 

 iridescent. 



Proc. Acad. Nat. Sci. 1861., p. 392. 

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