MIOCENE PECTENS. 65 



incremental lines; hinge line less than one-half length of the disk; anterior ear 

 slightly longer than posterior, arcuate-ended, and ornamented above the bj'ssal area 

 b_y 4 or 5 prominent radiating riblets, which, with the byssal area, are crossed bj' 

 numerous tine concentric lines; posterior ear rectangularly truncated, and orna- 

 mented by several radiating riblets and numerous incremental lines. Left valve 

 somewhat similar to right, but with narrower, ridge-like ribs and the broader inter- 

 spaces sometimes showiiig a more or less prominent intercalarj' riblet in the later 

 stages of growth; surface, when perfect, microscopically tessellated; ears radiately 

 and concentrically sculptured. 



Drmensions.— Alt. 93 mm.; long. 93 mm.; hinge line 38 mm.; diameter 12 mm. 



One of Conrad's cotypes from the Miocene of Astoria, Oreg. (U. S. Nat. Mus., 

 154155), shows the ribs and surface of the disk in a perfect state of preservation. 

 The ribs on the right valve are broad, squarish, and all moi'e or less mediallj^ sul- 

 cated, and with the surface sculptured by tine lines of growth and microscopic 

 tessellations. The left valve shows more or less prominent intercalaries in each 

 interspace, and has the whole surface beautifuUj' tessellated. 



This species has been confused by some authors with /■". cmirinus Gould, from 

 which it diflers by being smaller, more convex, and having fewer (15 instead of 

 20j ribs, and a tessellated surface on the left valve. 



P. propatuhis- is common in the Astoria Miocene of the Columbia River. A 

 specimen probably of this species, having 15 primary ribs on each valve, intercalary 

 riblets in most of the interspaces, and the typical tessellated surface, was found at 

 Newport, Yaquina Bay, Oreg. 



A variety of P. jm//uitv7ii.s, with possibly an average of one or two more ribs/ 

 and the intercalaries and medial sulcations slightly more prominently developed, 

 is found at Griswoldsville, San Benito County, Cal., and at several other local- 

 ities in the southern Mount Dia})lo Range. At Griswoldsville P. ptxrpatulm is 

 associated with the following species: PJiacoldea acutilineutiis, Area canal/.s, Pmiopea 

 generosa, Cryptomya calif ornica, Nucula castreTisis, Sigaretns sp., Trochita filosa^ 

 Dosinia sp. (thin. Hat). 



A more or less close relationship appears to exist between P. jn'opatulus, 

 P. oireni, and P. hetdciji. The last is distinguishable by its more numerous ril)s 

 (having generally 20 or more), and P. oweni by its much stronger intercalaries and 

 deeper medial sulcations. P. propahdtis is found in a horizon which is probably 

 somewhat lower than any in which either P. miji:rii or P. healeyl occur. 



Miocene (middle? and upper?). Clallam Bay, Strait of Fuca, Washington (Diller; 

 Arnold); Astoria, Oreg. (Dana; Dr. H. C. Kinney, and others); Newport, 

 Yaquina Bay, Oreg. (H. Hill); Point Simpson, B."c. (No. 3518, Cal. Acad. 

 Sci. Coll.); Griswoldsville. San Benito County, Cal. (Turner, Cooper). 



17260— No. 47— Oti 5 



