PLIOCENE PECTENS. 



115 



'.S 



except for ears, rather thin, and with smooth margins. Right valve with about 

 25 to 30 angular smooth-topped, imiiricated ril)s, whieh ])ecome diehotomous after 

 reaching a length of about 30 millimeters; interspaces deeply channeled and 

 narrower than "ribs; anterior ear imperfectly radially ribbed with C ridges, and 

 showing elevated, concentric incremental lines; posterior ear nearly obsolete, 

 showing about i ribs: byssal notch not deep. Left valve with 2.5 to 30 narrow, 

 convex ribs, showing imbricating sculpture only slightly; interspaces as wide as or 

 wider than ribs; after a diameter of 30 millimeters has Ixmmi reached by the left 

 valve small intercalary ribs appear in most of the widening interspaces; anterior 

 ear with 5 narrow, irnbricated ridges separated by wide interspaces. Both valve.- 

 show a tendency to contract suddenly at the })asal margin upon nearing comple- 

 tion of growth; surface of both valves covered with a minute lattice-like sculp- 

 ture, which is generally worn off on exposed portions of the shell. 



'Dlmemions.— Alt. 45 mm.; long. 42 mm.: hinge line is nun.; diameter 15 mm. 



This species is allied to the group of which /'. Ishmdleux is the type. 

 Although distinctly separated from the other members of the group, it is, never- 

 theless, quite closely related to /'. liaxtatiix var. nararchux and var. hliHlxi;. 

 The right valves of /'. jnnlani and of the two varieties above nu^ntioned are 

 very shnilar, but the l(>ft valve of /'. jordai,: is entirely different from that of 

 the other two, having simple, lattice-like sculptured ribs instead of imbricated, 

 fasciculated ones. P. Jordan! is distinguishable from /'. hoKtatus, and the latter's 

 variety hericlm by its lack of fasciculated ribs. No gradation between P. jordmd 

 and othei- members of the group has been noticed by the writer, whereas in 

 nearly all the oth(>r cases a large series shows obvious intergradation between 

 the different forms. 



/'. )(irdiiiii is found in both the Pliocene and lower Pleistocene, but is not 



known as living. 



KANIiE. 



Pleistocene (lower San Pedro formation). Deadman Island, San Pedro; Santa 



Barbara (.\rnold). 

 Pliocene. Deadman Island, San Pedro (Bush, Wilson, Oldroyd, Arnold): Santa 



Bar>)ara; Pacific Beach, San Diego (Arnold). 



Pkctex (Chlamys) LATiAiitrrus Conrad. 



PI. XbVl, li.iis. 2, ill, '?,, iuid -All. 



1837. Pfctoi kUiaiiritus Conrad, Jour. Acad. Nat. Sci. Phila., vol. 7, 1S:!7, p. L>:W, pi. IS, ti^'. H^ 

 1842. Pnien laliauratus Conrad, Sowerl.y, Tlies. Conch., vol. 1, |.t. 1, lS4->, j.. .",7, ].l. 12. fi<is. 



20, 21. 



1X44-1847. T'lxien tunica Philippi, 1844;t7'. mesoHmeris Sowerby, 1847 (fiile Dall, 189S). 



1852. Pecten Uitiaurttiis Conrad, Reeve, Conch. Icon., vol. 8, 1852, pi. 1, fig. 5. 



1863. Pecten latiauntm Conrad, Carpenter, Brit. Assn. Rept., 1863, p. 645. 



1S88. Pevten latiaaritus Conrad, Kfipter and Kobelt, Conch.-Cab., vol. 17, pt. 2, Spondylus nnd 



Pecten, No. 163, p. 20:^, taf. 54, figs. 7 and 8. 

 1888. Pecten latiauritus Conrad, Cooper, Seventh Ann. Kept. Cal. St. Min., 188S, p. 257. 

 1892. Pecten latifiuritvs Conrad, Keep, West Coast Shells, 1892, p. 167. 



