102 TERTIARY AND (JUATERNARY PECTENS OF PALIKORNIA. 



DeHcnpt'iDti. Slicll ;i\criigino- about 15(i iiiillinu'tors in altitudo. slij^htly 

 k)iii;of than liio-li. valves niiicli coiiipivsscd (tlio i-ii>ht ycniM-ally slightly nioro 

 convex than the left), etiiiihiteral. and with smooth margins; sides straight 

 or only slighdy coiuaxe ahove. Right valve with '_'(» to 25 strong, flat-topped, 

 squarish ribs, which, in some well-preserved specimens, show faint obsolete radial 

 stria'; interspaces llat-bottomed and about e(|ual in width to the ribs; whole 

 surface of disk sculptured by tine incremental lines; hinge line less than one- 

 half length of disk; antei'ior ear oidy very slightly longer than posterior, 

 ornamented with tine, sharp, incremental lines, but generally having no radial 

 sculpture whate\er; byssal notch prominent; posterior ear rectangular behind, 

 and with sculpture similar to anterior. Left valve slightly less ventrieose than 

 right, with narrow rounded ribs and wide concave-bottomed interspaces; surface 

 ornamented by' line, regular, raised, wavy, concentric lines, and sometimes more 

 or less tesselated; ears o])li(iuely truncated and sculi)tui'ed with sharj) incremental 

 lines and souK^times by obst)let(> radiating ridges. 



It'iiinnxitinx. — Alt. 105 mm.; long, llo nun.; hinge line 4S mm.; diameter 

 15 imu. 



The measurements are for a specimen considerably under the a\erage in si/e. 



This .species has cau.sed considerable confusion in the nomenclature of the 

 AVest Coast. In 1855 Conrad described a couple of small light valves of /'. caiirhiHii 

 and named the s\n\'wH " Pt'cfeii I/ee?'mann!.^' The following is his original descrip- 

 tion and notes (see synonym}' above): "Suborbicidar. thin, compressed; ribs about 

 •21. square, smooth; ears moderate in size. Locality, California. Doctor Heerniann. 

 Allied to 7*. fhareus of the Virginia Miocene, but very distinct; onlj- two inferior 

 valves were obtained; slightly convex." The type of P. Ihermannl (so labeled 

 in Conrad's own writing), and the other specimen referred to in the descrii)tion 

 are now in the Philadelphia Academy of Sciences, where they were examined and 

 photographed by the wiiter. They are both right valves of young P. cmtrinun 

 and undoubtedly came from the unique bryozoan marl of Santa Barbara, both 

 specimens showing the characteristic matrix and blue-gray color of specimens 

 of /*. caurinus from that locality. Some time after 1855 Conrad labeled a 

 /'. ixfrellaints and also some fragments of P. m!(iiieleni<v< in the National Mu.seum 

 with the name "■/'. /f^crmaniii.'^ One of the.se latter specimens is referred to 

 by Doctor Dall (see Dall, ISitS and 1901) as the type of /-". fleermanni. This 

 error of Conrad's caused Dall to apply the name "'Heermanni" to P. eittri'llaiins. 



The type of /'. JfccHi Conrad is in the National Museum (No. 13333) and 

 has been examined liy the writer. It, also, is a /*. <ai(r/7ius from the bryozoan 

 marl of Santa Barbara. The '"San Raphael Hills," from whence the type of 

 /*. Mi-il-11 came, according to Conrad, are neai' Santa Barbara. 



/'. Yi'Km/ciii'i.t Jay, from Amori. Kikonoken. -Japan, ilifl'ers from J', aittrmua 

 by having a more convex shell, wider, lower, more rounchHl ribs on the right 

 valve, less prominent ril)s on the left valve, and by having larger ears, which 

 are truncated more nearly at right angles. 



/■". caufi/nif ranges from tlie Pliocene upward. It has been reported from 

 the .Miocene by several authors, but so far none of these records have been 

 authenticated. 



