SCAMMON : THE UNIONISE OF KANSAS, PART I. 331 



Genus SYMPHYNOTA Lea, 1829. 



"Shell elliptic rhomboid, compressed ; beaks low, sculpture 

 consisting of strong bars ; one pseudocardinal in the right 

 valve and two in the left, the hinder somewhat A-shaped, 

 cutting off the hinge plate in the right valve ; laterals gener- 

 ally imperfect. 



"Animal with the gills semicircular below, inner the larger, 

 filling nearly the whole length from the abdominal sac ; mar- 

 supium thick, pad-like, filling the outer gills ; mantle strongly 

 attached at pallial line ; branchial opening papillose ; anal 

 opening without papillae." (Simpson.) 



Symphynota costata Rafinesque. Plate LXXVI, fig. 1. 



Alasmidonta costata Rafinesque, Ann. Gen. Sci. Brux., v, 1820, p. 318, 



pi. lxxxii, figs. 15, 16. 

 Alasmodonta rugosa Barnes, Amer. Jour. Sci. and Arts, VI, 1823, p. 



278, pi. XIII, fig. 21. 



Shell large, elongate oval, moderately thick, compressed in 

 male, less so in female. Anterior margin an abrupt curve ; 

 anterior portion of ventral margin gently curved, posterior 

 portion straight ; posterior margin roundly biangulate ; dorsal 

 margin straight or slightly curved. Umboidal ratio, from 

 0.25 to 0.30. Umbones flat and low, marked with three very 

 coarse, parallel ridges. Umboidal slopes all flatly rounded, 

 the posterior slope marked with a series of moderate-sized 

 undulations which are curved slightly upward anteriorly. 

 Lines of growth coarse, numerous, continuous. Epidermis 

 horn color to deep brown. Ligament long, dark brown. 



Interior: Pseudocardinals large, erect, serrate, double in 

 the left and single in the right valve. Lateral teeth indi- 

 cated only by an indistinct broken ridge on each hinge plate. 

 Anterior scars rather large, smooth ; adductor cicatrix deeply 

 impressed in its dorsal portion ; retractor cicatrix lightly im- 

 pressed and generally fused at the anterior end with the 

 adductor cicatrix. Posterior scars large, lightly impressed, 

 fused. Dorsal cicatrices a row of small scars almost at the 

 base of the pseudocardinals. Pallial impression sometimes 

 well marked. Cavity of the umbones slight, of the shell 

 moderate. Nacre rich cream color in the cavity of the shell, 

 white marginally, iridescent posteriorly. 



