DESCRIPTIONS OF TWO NEW SPECIES OF THE GENUS UNIO, 

 FROM THE OZARK REGION OF MISSOURI. 



By R. ELJLSWORTH CALL. 



(Plates XXVII, XXVIII.) 



The collections in which these forms occurred were made in July, 1886. 

 The associated species were Unio iris Lea, Margaritana deltoidea Lea, and 

 abundant, though as yet undetermined Strepomatidcc, of the genus Gonio- 

 basis. The streams were characteristic of mountain areas, being shal- 

 low, swift, and limpid, with rocky bottoms. In occasional ponds, occupy- 

 ing depressions which were filled at seasons of floods, were found nu- 

 merous examples of Unio subrostratus Say, and Anodonta grandis Say, 

 both of which were remarkable for their large size and perfect condi- 

 tion. It should be further noted that the streams from which these 

 shells came, form a portion of the southern drainage of the Ozarks. 



Unio ozarkensis, sp. nov. (Plate xxvii, Figs. 1-3 <?, 4 $). 



Shell smooth, elliptical, somewhat compressed laterally, inequilateral, 

 thick, but thickest anteriorly; epidermis thin, striate towards the 

 margins, yellowish-brown or olivaceous, marked with numerous obscure 

 narrow green rays disposed regularly over the central portion of the 

 disk ; lines of growth rather numerous, dark, well marked ; dorso-pos- 

 terior margin curved ; posterior umbonal slopes always eradiate, more 

 or less biangulate, which angulations continued posteriorly mark the 

 siphonal area and render the posterior margin triangular ; umbones 

 small, triangular, scarcely prominent, approximating, marked in non- 

 eroded specimens by two or three rather coarse undulations; liga- 

 ment short, thick, light brown ; cardinal teeth disposed to be double 

 in both valves, short, oblique, thick, unequally bifid, striated, the pos- 

 terior division generally thickest and heaviest ; lateral teeth rather 

 short, slender, slightly curved, crenulate at extremities, in general di- 

 rection forming nearly a right angle with a line drawn through the tip 

 of the umbo and the anterior division of the cardinal tooth ; anterior 

 cicatrices deep, pit-like, striate, confluent, though in occasional speci- 

 mens the > protractor -pcdis impression is distinct from the adductors and 

 deep ; posterior cicatrices distinct, that of the adductor muscle being 

 usually well impressed, that of the retractor-pedis muscle circular, pit- 

 like, impresed at extreme end of lateral tooth ; pallial cicatrix well im- 

 pressed throughout, but especially marked anteriorly ; dorsal cicatrices 

 irregularly crowded and placed near the inferior edge of the plate which 

 connects the lateral and cardinal teeth ; nacre usually silvery white, 

 occasionally salmon or warm pink, iridescent posteriorly. Length 

 5450mm. breadth 15.28 mm ; height 32.7G mju . 

 498 



