3f'2 KANSAS UNIVERSITY SCIENCE BULLETIN. 



continuous. Ligament thick, dark brown. Lunule long and 

 narrow. 



Interior: Pseudocardinals high, pyramidal, ragged, single 

 in the right and double in the left valve, the right pseudo- 

 cardinal being surrounded by a shallow, rounded ditch. Lat- 

 erals straight or curved, long, high, oblique. Interdentum 

 variable, cut away for the right valve to receive the left 

 posterior pseudocardinal. Anterior adductor cicatrix semi- 

 circular in outline, fairly deep. Posterior cicatrices slightly 

 larger than the anterior ones, well marked, coniluent. Pal- 

 lial line well impressed for its anterior two-thirds. Dorsal 

 scars a row of pits on the lower surface of the interdentum and 

 pseudocardinals. Cavity of the beaks large and deep, of the 

 shells moderate. Nacre pearly white, iridescent posteriorly. 



Q. lachrymosa is found in the St. Lawrence basin and the 

 Mississippi drainage. It ranges southwest into Texas. Ii Is 

 a common species in all the Kansas systems and particularly 

 abundant in the eastern Kansas drainage. It has been re- 

 ported as far west as the Smoky Hill river at Salina. This 

 species is not at all choice as to habitat. It often rivals 

 Obovaria ellipsis as a habitant of sand-bars, and is also found 

 in mud or shingle in water of variable depth. 



The shell is as variable as its environment. The epidermis 

 may be greenish yellow or dark brown, the tubercles numer- 

 ous and erect or few and obscure. The size of the adult shell 

 i- also a variant. The shells of the animals living in muddy 

 stations are large and massive ; those from sand-bars thinner 

 and smaller. The author found in a large series of material 

 taken from beds of shingle in the Wakarusa river that the 

 mean relation of the length to the height was 1.110: 1.000. 

 The extremes were 1.029 : 1.000 and 1.218 : 1.000, respectively. 



The chief distinctions between this and other members of 

 the lachrymosa group will be found under Q. aspera and 

 Q. fragosa. 



