92 TERTIARY AND QUATERNARY PECTENS OF CALIFORNIA. 



smaller. :ind having the ribs reach to or nearly to the periphery rather than 

 abruptly terminating near the middle of the disk. 



The type .specimen, which is the one figured, is now in the collection of 

 Delos Arnold. It is from the buff-colored ^Miocene shale in a small ravine on 

 the Burke ranch, one-third mile south of Los Tranco.s Creek, near Stanford 

 University, San Mateo County. This species is named in honor of Leland 

 Stanford Junior University. 



So far this species has been found only in the type locality, where it is 

 associated with Pccten 2)edroanus (?) and several small undetermined pelecj^pods. 

 Its range, as determined stratigraphically, is probably middle Miocene or Monterej\ 

 Its associated fauna also adds weight to this theory. 



Miocene (middle). Burke i-anch, 3 miles south of Stanford University (Branner, 

 J. P. Smith, R. Arnold). 



PeCTEN (AmUSIUM) LOMFOCENSIS n. sp. 

 PI. XXVIII, figs. 1, 2, and S. 



Description. — Adult shell averaging about 100 millimet(M-s in altitude, somewhat 

 longer than high, compressed, subcqui valve, equilateral, and thin; liase regularly 

 rounded; sides straight, or nearly so; margins smooth. Right valve with external 

 surface smooth except for veij tine and luuiierous concentric and nearly obsolete 

 radiating stria-; internal surface sculptured by about fourteen pairs of rather 

 prominent rounded radiating lira?, the members of each pair being separated by 

 flat .spaces usually of about two-thirds the width of the luajor interspaces (in 

 one case the .spaces between the members of each pair were as wide as the 

 interspaces); hinge line about two-fifths the length of the disk; ears subequal, 

 obliquely truncated, and fin(>ly concentrically sculptui'ed; anterior with a faint 

 suggestion of a byssal notch; ctenolium absent. Left valve similar in all respects 

 to the right except that the anterior ear has a straight, rather than an arcuate end. 



Dimensions. — Alt. 103 mm.; long. 113 mm.: hinge line 40 mm.; diameter 

 20 mm. 



This very unicjue species, of which there are no closely allied forms in the 

 Tertiary or living faunas of the west coast, so far as known, is somewhat 

 analogous to P. (Ammium) mortoni Ravenel of the Miocene and Pliocene of 

 eastern America. It is distinguishable from the latter species, however, by the 

 smaller number, greater prominence, and more regular arrangement of the 

 internal ribs. P. loinjjocensis is included in Amnsinm, because it appears to 

 show stronger affinities for this than for any other group. 



P. lonqxK-ensis was first discovered in the lim_v beds which outcrop about 4 

 miles south of Lompot', Santa Barbara County, where the types, which are now 

 in the collection of the California Academy of Sciences, were collected by Mr. 

 Frank M. Anderson. At the type locality this unique form is found associated with 

 the following species in beds of probable lower Miocene age: Pecten erasslcardo, 

 Ostrea (of.) titati, Lima n. sp., Oidaris (?) sp., Terebratella 2 sp., and Scutella 



