SCAMMON : THE UNIONID.E OF KANSAS, PART I. 287 



Call has suggested (5) , the difference between the two forms 

 is probably dependent directly on individual habitat. 



The sexual dimorphism is particularly striking, the in- 

 flated and sometimes posteriorly truncated females being 

 readily distinguished from the longer and more flattened 

 males. The decided variation in the color of the epidermis 

 and the number and prominence of the lines of growth bear 

 no relation to the sex. There is some variation in the thick- 

 ness of the shell. 



Lampsilis luteola Lamarck. Plate LXIV, fig. 2. 



Unio luteola Lamarck. An. sans Vert., VI, 1819, p. 79. 



Shell large, of variable thickness, subelliptical, males 

 slightly inflated, females decidedly so. Anterior margin 

 rounded ; ventral margin straight, often slightly bowed, much 

 produced posteriorly in the female ; posterior margin bluntly 

 rounded in the male and obtusely angulate in the female ; dorsal 

 margin almost straight and meeting the posterior at an angle 

 of from 145 to 150 degrees. Umboidal ratio from 0.15 to 

 0.25. Umbones prominent, somewhat inflated, marked by 

 from eight to sixteen sharp undulate ridges. Epidermis 

 smooth or rough, according to station, lines of growth promi- 

 nent and continuous, color variable, generally straw yellow, 

 sometimes rayed over the posterior portion of disk with bands 

 of sage-green of variable thickness and frequency. Ligament 

 stout, long, deep brown. 



Interior: Pseudocardinals high, lamellar or columnar ser- 

 rate, directed anteriorly, two in the left valve and one (and 

 sometimes two) in the right. Laterals of moderate length, 

 thin, highest posteriorly, slightly curved. Anterior adductor 

 cicatrix large, well impressed, variable as to shape, but 

 much longer than wide, retractor cicatrix large and well im- 

 pressed. Posterior scars large, lightly impressed, often fused. 

 Dorsal scars small, pits scattered over the cavity of the um- 

 bones. Pallial line well impressed anteriorly and well marked 

 posteriorly. Cavity of beaks shallow, of shell rather large. 

 Nacre white, sometimes slightly iridescent posteriorly. 



