ARNOLD — TUE I'ALEONTOLOCiY AND STUATUilUrilV OV SAN I'EDRO. HI 



Distinguishable by the few prominent, sulcated ridges, and smooth surface, 

 except for minute sculpture. Specimens identified by Dr. Dall. 



Two specimens from the lower San Pedro scries of Deadniari Island, one of 

 which is figured, and is now in the collection of Delos Arnold. 



Living. — Unalatika (Dall). 



Pleistocene. — Alaska (Dall): San Pedro (Arnold). 



30. Pecten (Chlamys) jordani, sp. nov. 



Tlate XII, Fios. AM) 7. 



Shell of medium size, shape of P. hericeus, inequivalve, rather thin; right valve with twenty- 

 five to thirty angular, smooth-topped, imbricated ribs, which become dichotomous after reaching a 

 length of about 30 mm.; interspaces deeply channeled and narrower than ribs; anterior ear imper- 

 fectly radially ribbed with six ridges, and showing elevated, concentric, incremental lines; posterior 

 ear nearly obsolete, showing four ribs; byssal notch not deep; left valve shows twenty-five to thirty 

 narrow, convex ribs, showing imbrications only slightly; interspaces as large as ribs; after a diameter 

 of about 30 mm. has been reached by the shell, small riblets appear in the widening interspaces; 

 anterior ear shows five narrow, imbricated ridges, with wide interspaces; both valves show a tendency 

 to contract suddenly at the basal margin upon nearing completion of growth ; surface of both 

 valves covered with a minute, lattice-like sculpture, which is generally worn off on exposed portions 

 of the shell. 



Dimensions. — Long. 42 mm.; alt. 45 mm.; diam. 15 mm.; hinge iS nun. 



Allied to P. ojmntia Dall, but having fewer ribs on disk and ear, and having 

 dichotomous ribs after reaching a diameter of 35 mm. Distinguished from P. hericeus 

 and P. hastaius by not having fasciculated nor spinose ribs. 



Rare in Pliocene of Deadman Island and lower San Pedro series of Deadman 

 Island. Found also in Pliocene of Packard's Hill and Pleistocene of bath-house, 

 Santa Barbara. 



The specimen figured is the type, which is from the Pliocene of Deadman 

 Island and is now in the United States National Museum. 



Pleistocene. — San Pedro, Santa Barbara (Arnold). 



Pliocene. — San Pedro, Santa Barbara (Arnold). 



31. Pecten (Chlamys) latiauritus Conrad. 



Plate XII, Fics. 2 and 2a. 



Pecten latiauritus Con., Jour. Phil. Acad. Sci., Vol. VII, 1837, p. 238, PI. XVIII, fig. 9. Reeve, 

 Conch. Icon., PI. I, sp. 5. Sowerby, Thes. Conch., PI. I, p. 57. Carpenter, Brit. 

 Assn. Rept., 1863, p. 645. Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 257. 

 Keep, West Coast Shells, p. 167, 1892. Williamson, Proc. U. S. Nat. Mus., Vol. 

 XV, 1892, p. 193; ^ P. tunica Phil., 1844, -\- P. mesotimeris Sowerby, 1847 {fide 

 Dall, Trans. Wagner Inst. Sci., Vol. Ill, Part 4, 1898, p. 709.) 



Shell small, suboval, inequivalve, subequilateral, compressed, thin ; surface ornamented with 

 from twelve to fifteen squarish, elevated, distinct ribs, with about equal, channeled interspaces; ribs 

 often mesially grooved; hinge line wide, the ears pointed above. 



Dimensions. — Long. 25 mm.; alt. 23 mm.; diam. 9 mm.; hinge 20 mm. 



