90 TERTIARY AND QUATERNARY PECTENS OK CALIFORNIA. 



Pecten (Pseudamusium) pedkoanus Trask. 

 PI. XXVIII. tit:.«. 4 :iiicl 5. 



1856. Pliif/I(j.fli>iiia I'edroanii Trask, Proc. C'al. Acad. Nat. S(ti., vol. 1, lyStJ, j). 9;i, pi. 3, tigs. 1, la. 



1856. FUuiioKtoma trunmta Trask, Proc. Cal. Acad. Ivat. Sci., vol. 1, 18.56, p. 94, pi. 3, fig. 3. 



18.56. Plagiodama (innxlatux Trask, Proc. Cal. Acad. Nat. Sci., vol. 1, 18.56, p. 94, pi. 3, fig. 2. 



1869. Pecteti Pcdri>anHS Trask, Gabb, Pal. Cal., vol. 2, 1869, p. 60. 



1888. Pcclen jiciimanm Trask, Cooper, Seventh Ann. Kept. Cal. St. Miii., for 1887, p. 258. 



1898. PecU'ii pnlroaiiu.-! Trask, Dall, Trans. Wagner Free Inst. Sci., vol. 3, pt. 4, 1898, p. 705. 



The original description is as followfs: 



DeKcr'iptioii. — "Sbell compressed, subtrianouiar, with s or 9 tlatly rounded 

 concentric annulations, which are nearly as distinctly marked on the interior of 

 the valve for about half the height from the ventral margin; beaks acute at the 

 a])ex, and ns liigh as the line of the auricles; anterior aui'icle rounded in front, 

 and has a shiiiII, thin fold extending from the umbone to the center of its 

 anterior margin, and is covered with about 13 small, rounded, radiating 

 stria^, which converge at the beak; beaks at the anterior third; suljacute; anterior 

 margin rounded, and .somewhat produced; ventral margin smoothly arched; 

 posterior margin rounded, becoming slightly arcuate toward the dorsum of the 

 shell; posterior auricle angulate and obtusely truncate posteriorly." 



lJ!iiit'iiKli>ii.'<. — Alt. JiU mm.; long. 37 mm.; hinge line 13.5 mm. 



The above is Doctor Trask's original de.scription wnth measurements of the 

 type, (xabb has the following to say of this species:" 



"In LS5t) Doctor Ti'ask named three species of Playlostoniu, giving full 

 descriptions and well-executed figures as above. His specimens are casts of a 

 numb(M- of distorted J'ecft'/i.s, perhaps normallv a little oblique, but in most cases 

 with till- (ibliiiuity exaggerated by pressure. They belong without question to 

 but one species, and the first name given will have to l)e retained. I have 

 carefully studied the specimens, and have visited the locality from which the}' 

 were obtained. The deposit lielongs to the bituminous shale of the upper Miocene, 

 which underlies the whole or the greater part of the Los Angeles plain, crops 

 out on the beach at San Pedro, under the post-Pliot-ene. and has been reached 

 bj' artesian borings imder the city itself. 



"The species is about an inch in diameter, ears subequal, shell thin, perhaps 

 normally a little oblique, and the shell substance contains a few concentric 

 undulations or ribs, which are retained in the cast. No specimens show an_v shell 

 preserved; so that if there was any surface sculpture, it is as yet unknown." 



The writer has examined several specimens of this species collected by Mr. 

 W. L. AVatts in the oil fields of southern California. Some of these specimens 

 show the original shell material, which, upon a careful examination, revealed no 

 trace whatever of any but the concentric undulating sculpture. 



The best preserved specimens of this species examined b}' the writer were 

 taken from the Third street tunnel in Los Angeles by Mr. Homer Hamlin and 

 are now in the U. S. National Museum (No. 164840). In several of these specimens 

 the original shell material is (juite well preserved, and in one case CamptonecteH 



a Pal. Cal., vol. 2, 1869, p. 60. 



