TERTIARY MOLLUSCA. 133 



growth-lines visible on submargins and interspaces but eroded on ribs and 

 ears; 2 or 3 posterior ribs have distant curved imbricating lamellae convex 

 towards the beak; submargins convex, without ribs, not sharply differentiated 

 from the ears; ears depressed below the plane of the disk; left anterior ear 

 large, acutely oblique, with 4 strong, smooth ribs; left posterior ear small, 

 obtusely oblique, with 2 or 3 faint riblets. 



Bight valve equilateral, gently convex, with about 20 regular convex riba, 

 with nearly equal interspaces, in each of which appears a single thread; ribs 

 and threads of anterior end with distant, curved lamellae like those on the 

 left valve; minute, close growth-lines visible in interspaces of anterior end, 

 but eroded from the remainder of the valve. 



Long, of right valve, 30 mm. 



The right and left valves have been described separately because of 

 the possibility that they may prove to belong to different species. The 

 left valve is the type. 



Locality. — Crocus Bay, Anguilla, stations 6894 and 6965 (type), 

 Vaughan. 



Geologic horizon. — Oligocene. 



Type.—U. S. Nat. Mus. No. 167094. 



Pecten willobianus, new species. 

 (Plate 11, Figures 1, 2, 3.) 



The following is a description of this species: 



Shell equivalve, nearly equilateral, with 18 or 19 smooth, rounded ribs with 

 equal interspaces; interspaces with low riblets peripherally; submargins 

 smooth, convex, sharply delimited from the ears; ears large, smooth, except 

 the right anterior ear, which is radially ribbed; internal ventral margins with 

 short flutings in harmony with the radial sculpture. 



Alt., 30 mm.; lat., 29 mm.; diam., 10 mm. 



Locality. — Willoughby Bay, Antigua, station 6881, Vaughan. 

 Geologic horizon. — Oligocene. 

 Types.— U. S. Nat. Mus. No. 167119. 



Pecten vaughani, new species. 

 (Plate 8, Figures 2, 3, 4.) 



The following is a description of this species: 



Shell small, compressed, equivalve, equilateral, with 14 or 15 smooth, 

 rounded ribs on right valve, 15 to 17 on left, separated by nearly equal, 

 rounded interspaces; microscopic sculpture of fine, close, concentric lines ; 

 submargins smooth, steep; ears of left valve nearly equal, smooth, ears of 

 right valve unequal, anterior ear with about 5 radiating, scabrous riblets; 

 byssal notch one-half the length of the ear; posterior ear smooth. 



Alt., 16 mm.; lat., 16 mm.; diam., about 5 mm. 



Locality. — Crocus Bay, Anguilla, stations 6894 (type), 6893, 6965, 

 6967, Vaughan. 

 Geologic horizon. — Oligocene. 

 Type.—U. S. Nat. Mus. No. 167084. 



