TERTIARY MOLLUSCA. 139 



The following is a new description of this species : 



Shell orbicular, tumid, with 19 radiating ribs, simple to about 10 mm. from 

 the beak, but each with two lateral riblets on the mature part of the shell; 

 spaces between the ribs deep, concave, a little narrower than the ribs, set with 

 riblets near the periphery; surface covered with concentric imbrications which 

 are produced into blunt spines on top of the ribs and riblets; submargins with 

 numerous radiating riblets; ears rather large, with radiating threads and con- 

 centric imbrications. 



Alt., 21 mm.; lat., 23 mm.; diam., about 5 mm. 



Localities. — Crocus Bay, Anguilla, stations 6965 and 6967, Vaughan ; 

 Santiago, Cuba, station 5255, Black; Santo Domingo, Bowden. 

 Geologic horizon.-- Oligocene. 

 Type. — British Museum, from Santo Domingo. 

 Figured specimens.—V. S. Nat. Mus. Nos. 167069, 167070, 167071. 



Pecten (ASquipecten) jacobianus, new species. 



(Plate 11, Figures 7 a, b, 8.) 



The following is a description of this species: 



Shell equivalve, slightly oblique, moderately convex, with about 16 low, 

 broad, radiating medial ribs and several additional obsolete distal ribs; addi- 

 tional radial sculpture of raised threads, usually one on summit and one or 

 more on each side of every rib and one or two in the interspaces, increasing in 

 number by interpolation towards the periphery; concentric sculpture of low, 

 wavy lamellae, crossing ribs, threads, and interspaces; Camptonectes striation 

 present; posterior ears oblique, with faint radiating threads crossed by fine 

 lamellae; anterior ears the larger, with coarser threads; byssal notch about 

 one-half the length of the ear; ctenolium present; inner margin grooved in 

 accordance with the external ribbing, but grooves do not extend over the 

 medial portion of the disk. 



Alt., 29 mm.; lat., 27.5 mm.; diameter, 9 mm. 



Localities.— Santiago, Cuba, stations 3436, 3440 (type), 3443, 3447, 

 Vaughan. 



Geologic horizon. — Oligocene. 

 Type.—U. S. Nat. Mus. No. 167115. 



Pecten (Plagioctenium) crucianus, new species. 

 (Plate 10, Figures 8, 9 a, 6.) 



The following is a description of this species: 



Shell suborbicular, slightly oblique, moderately convex, with nearly equal 

 valves and 20 to 22 convex ribs with equal interspaces, each containing 1 

 riblet; near the periphery 1 riblet is developed on the summit of each rib; 

 submargins faintly ribbed; entire disk covered with minute, close, concentric, 

 raised lamellae, fused on the summits of the riblets into evenly spaced, raised, 

 transversely elongate nodes; anterior ears the larger; right anterior ear witn 

 about 5 strong riblets, other ears with many fine riblets; posterior ears oblique; 

 byssal notch deep; internal surface channeled in harmony with the external 

 ribbing. . 



Alt., 35.4 mm.; lat., 35.4 mm.; diam. of left valve, 7.4 mm. 



