MIOCENE PEOTENS. 61 



intorcalary is often quite prominent; whole surface sculptured by inconspicuous 

 incrcMueutal lines; hinge line more than one-half length of disk; ears equal, some- 

 what convex, rather obliquely truncated and turned up slightly at the corners; 

 sculpture of ears consists of fine incremental lines; byssal notch rather small. 

 Left valve flat, with a slight tendency toward concavity near the umbo, with 

 broad lateral areas and with 18 or 19 low, rather flat-topped ribs; interspaces 

 somewhat wider than the ribs; surface sculptured by line incremental lines; ears 

 concave, obliquely truncated and sculptured by more or less irregular concentric 

 lines. 



Dimensionii. — Alt. 75 mm.; hinge line to ventral margin 72 nun.; long. 82 mm.; 

 hinge line 35 mm.; diameter 20 mm.; umbonal angle (left valve) 102'-'. 



This species is distinguishable from P. vugdeni and /'. exccvimttm, which it 

 resembles in general characteristics by its greater relative length, somewhat less 

 convexity, greater uinl)onal angle, broader lateral areas and lower ribs. 



This species is found associated with P. camzoenxis and (>.itrea respertiua in 

 beds in the Carrizo Creek district which are probably of Miocene age. The 

 type is from Alverson Canvon, San Diego County, and is now in the collection 

 of Delos Arnold. Named in honor of Prof. Josiah Keep, of Mills College, whose 

 works on California conchology have greatly stimulated the study of that subject 

 on the Pacific coast. 



Miocene. Eight miles north of Mexican boundary, in Alverson Canyon, Carrizo 

 Creek district. San Diego County (Bowers); Santa Rosalia, Lower California, 

 west of and directly across the Gulf from (hiaymas, Mexico (E. Palmer). 



Pkcten (Patinopecten) coosensis Shumard. 



PI. VI, fig. 2; PI. VII, ligs. 2 and 2ii. 



1858. Pecten coosensis Shumard. Trans. St. Louis Acad. Sei., vol. 1, pt. 2, 1858, p. 122. 



18fi4. Pecten coosnensis Shumard, Meek (typ. err.), Miocene check list, Smithsonian Miscell. Coll., 



1864, p. 3 (./iV?e Dall, 1898). 

 1869. Pecten coosensis Shumard, Gabb, Pal. Cal., vol. 2, 1869, p. 122. 

 1898. Pecten {Paliiiopi'cten) coosensis Shumard, Dall, Trans. Wagner Free Inst. Sei., vol. 3, pt. 4, 



1898, p. 700, pi. 26, tig. 2. 



Bencri.ptlun. — Shell averaging about 110 millimeters in altitude, slightly longer 

 than high, valves both well compressed, equilateral, and with margins smooth; sides 

 only slightly concave, and sloping at only a moderately low angle. Right valve with 

 21» to 31 prominent T-rail shaped ribs, flattened and sometimes faintly dichotomous 

 above, overhanging narrow, deep, almost flat-bottomed channels; whole surface 

 .sculptured with more or less prominent fine concentric lines; hinge line nearlj' 

 equal to one-half length of disk; anterior ear slightly produced and sculptured by 

 radiating ridges and imbricating concentric lines; byssal notch wide and deep; pos- 

 tei'ior ear rectangularly truncated, and sculptured bv sharp incremental lines and 

 sometimes hy obsolete radial ridges. Left valve with narrower, rounded, concave- 

 sided ribs and wider, round-bottomed interspaces; sculpture of numerous, sharp. 



