i2 Bulletin 24 50 



lines which are here rather closely crowded. Left valve (not 

 well preserved in type specimen) with seven or eight very wide 

 ribs, separated by narrow and deep interspaces. 

 Length 70, width 68, thickness 18 mm. 



The specimen above described is from the Cornell Univers- 

 ity collection and labelled as Miocene of Lake Waccamaw, N. C. 

 When more is known concerning its exact stratigraphic posi- 

 tion the species may prove to be Pliocene, as is also the case with 

 Modiolus gigantoides. The specimen is not well preserved, being 

 a large cast, with a portion of the shell of the left valve still re- 

 maining. Three of the ribs are much more prominent than the 

 other four, but apparently all were introduced at about the same 

 time. These three ribs, together with the rather angular submar- 

 gins, give the shell a quinquecostate appearance. 

 Miocene {?); Lake Waccamaw, JV.C, 



Modiolus pulchellus, n. sp., Plate 4, Fig's 12-14 



Shell small, smooth, convex ; beaks low ; anterior end very 

 short, posterior slope even, not depressed ; posterior end of hinge 

 line evenly rounded into the base ; anterior margin with a slight- 

 impressed zone ; surface smooth , with incremental concentric lines 

 which are occasionally deep and then represent resting stages ; 

 ligamental sulcus deep and narrow, with finely crenulated edges. 



Length p, width 6.5, thickness j. 3 ?nm. 



This species in its general shape recalls M. silicatus Dall (as 

 M. tampaensis, PI. 27, fig. 28) of the Upper Oligocene of the silex 

 beds at Ballast Point , Florida but is a smaller shell. The posterior 

 extremity in M. silicatus according to Ball's figure appears to be 

 slightly depressed and with the anterior margin wide and flat. In 

 the Miocene shells the anterior margin carries a small tooth-like 

 projection. The crenulation of the ligamental sulcus is also a con- 

 stant character and is well-marked in both valves. Shell generally 

 thin but occasionally quite heavy with deep muscle scars. 



Yorktown formation : Kingsmill {type) , Grove Wharf. 



