21 St. Maurice and CIvAiborne Pelkcypoda 21 



the lateral umbonal margins ; surface ornamentation, imbricate 

 concentric lines ; ribs often showing an incilnation to bifurcate on 

 marginal areas, at least a deeply incised line is often seen on the 

 tops of the ribs in these regions ; near basal margin there is a 

 tendency to show obscurely, however, three raised lines on top of 

 main ribs and one or three lines in the inter-costal area. 



Left valve while young showing markings similar to those 

 described above, with more nearly equal ears, however, and a 

 tendency to show at an earlier age three lines on top of the ribs; 

 and a strong line (often between two others) between the ribs , 

 irregularities like subdivision of costse, increasing comparative 

 width of interradial spaces, great increase in radiating, fimbriate 

 lines on top of ribs on their sides and in interspaces, apparent: 

 shell deepening rapidly with age. 



Occasionally on certain portions of the exterior of the left 

 valve a strong, bi-partite structure is seen in the ribbing. This 

 has given rise to the varietal name tirm^is \>y de Gregorio. We 

 do not think it of even varietal rank . 



Concerning the t5''pe of deshayesi in the Phila. Acad, it may 

 be notedvthat it shows 20-22 primary, with as many inter-ribs ; 

 the latter apt to be on the anterior side of the intercostal 

 space ; traces of tertiary riblets ; few signs of riblets superim- 

 posed on primary ribs ; finel)^, evenly crinkled, concentric in- 

 cised lines on ears. 



The type specimen of lyelli has about an equal number of 

 ribs ; but slight traces of intercostse and concentric line ; ribs not 

 showing bifurcation as plainly as is indicated by fig 7, pi. 13 

 of this work. 



Types. — Philadelphia Acad. Coll., Cat. Nos. 5425, 5426. 



Localities aiid Horizon. — Typically in the Claiborne sand 

 horizon. A specimen seemingly of the lyelli form is in our col- 

 lection from the Orangeburg district, S. C. 



Specimens figured. — Collections at Cornell Univ. 



Pecten wautubbeanus Dall, PI. 14. Figs, i, 2, 3, 4. 



P. {Chlamys) wahtubbeanus Dall, Trans. Wag. &c, 1898, vol. 3, p. 

 736, pi. 34, fig. 9. 



