1 6 Bulletin 24 54 



and these are separated from each other by impressed lines ; these 

 radial threadlets become much narrower on the anterior submar- 

 gin, obsolete on the posterior dorsal slope ; concentric sculpture 

 of evenly spaced, distant, high lamellae, becoming lower and more 

 closely spaced on the umbo ; on the posterior dorsal slope the la- 

 mellae are more crowded, wavy and irregular in direction, but 

 show little or no compression; the radial threadlets are continued 

 on the lamellae and end just below the top; the lamellae are there 

 fore not crenulated. 



Length j6, height 44., depth of valve 9 mm. 

 This fine shell belongs to the group of Semeles represented in 

 the Oligocene by 5". chipolana Dall and perlamelloides Maury and 

 in the Pliocene by .S". leana Dall and 6". perlamellosa Heilprin. 

 The only species with which comparison is necessary, is 5". 

 leana, which has much the same contour. In the Miocene shell 

 here described, the concentric lamellae are much less numerous, 

 higher, and more distantly spaced, the radial threadlets coarser, 

 and these do not crenulate the concentric lamellae. The posterior 

 extremity of 6". leana is markedly truncated and with the poster- 

 ior dorsal slope strongly depressed; and here the concentric lamel- 

 lae are low, crowded and flattened. 5". perlamellosa on the other 

 hand, is more nearly equilateral, more elongated and with the 

 sculpture much like .S. leana. 



Duplin formation ; Peedee river f S. C. 



Petricola (Claudiconcha) grinnelli, n. sp. Plate 4, Fig's 7-10 



Shell elongated, solid, often distorted ; anterior end rounded; 

 posterior end elongated, pointed ; right valve slightly larger and 

 overlapping the left, especially on the posterior, dorsal margin ; 

 surface sculpture of irregular, radial striae, which as a rule, are 

 slightly larger and separated by wider interspaces on the anterior 

 portion of the shell ; striae more or less granulated by concentric 

 lines : hinge weak, with slender teeth, those in the specimens 

 broken off, but, judging from the stumps remaining, consisting 

 of three cardinal teeth in each valve. 



Type specimen : Length 22, height ij, thickness 12, mm. 

 A la? r ge valve : Length 25 , height s6, thickness 7 mm. 



The subgenus Claudiconcha Fischer as exemplified by P. ?no?i- 



