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University of California Publications in Geology [Vol. ll 



P. fucanus Dall 100 is of the same general type as P. gabbi; it differs 

 from this form in that it has a less number of ribs, the interspaces are 

 wider, and the radial striations, seen on the ribs of the former, are 

 lacking on the latter. 



PECTEN (PSEUDOMUSEUM) ALTERNILINEATUS, n. sp. 

 Plate 13, figures 14 and 15 

 Type specimen 11203, Coll. Invert. Palae. Univ. Calif., loc. 1131 

 Pecten peckliami Clark, Univ. Calif. Publ., Bull. Dept. Geol., vol. 9, no. 2, 

 p. 14, 1915. 



Shell small, thin, subeireular, compressed, equivalved, nearly equilateral. 

 Apical angle close to 90°. Surface covered by numerous fine, radiating, raised, 

 bifurcated lines, which are nearly obsolete on most of the specimens examined, 

 interspaces between the lines averaging a little wider than the width of the lines. 

 Posterior ear of right valve not separated by a well-defined line from main surface 

 of shell; posterior edge of ear straight, sloping outward; surface smooth on 

 specimens at hand but probably originally radially sculptured, similar to that 

 on the main surface of shell. Anterior ear of right valve very distinct, with 

 a rather deep and acutely angular byssal notch; surface of ear covered by about 

 five subnodose to spinose radiating lines. Ears of left valve similar to those of 

 right except that anteriorly there is no byssal notch. 



Dimensions. — Type specimen : length, 5 mm. ; height, 5.5 mm. ; diameter of 

 both valves, 75 mm.; paratype: length, 5.5 mm.; height, 6 mm. 



Occurrence. — University of California locality 1131. 



Pecten alternilineatus is about the same size and belongs to the 

 same general type as P. vancouverensis Whiteaves, 107 from which it 

 differs in the following respects : The radiating lines on the main 

 surface of the shell are not so numerous nor so closely crowded; the 

 ears are larger and the radiating sculpturing is not so coarse ; the 

 hinge line is longer in proportion to the width of the shell, and the 

 margins below the ears are less convex than on P. vancouverensis. 



Pecten alternilineatus resembles rather closely P. peckhami Gabb, 108 

 a common species in the Lower Miocene of the West Coast, from which 

 it differs as follows : On the left valve the ears are considerably nar- 

 rower in a dorsal-ventral direction, and in the vicinity of the anterior 

 ear the swell of the main surface of the shell commences as an inclined 

 slope rather than at right angles, as is the case on P. peckhami as 

 described by Gabb ; the anterior edge of the anterior ears comes out 



106 For original description of P. fucanus see Trans. Wagner Free Inst. Sci., 

 vol. 3, pt. 4, p. 704, pi. 26, fig. 7, 1898. For good redescription, see Arnold, 

 U. S. Geol. Surv., Prof, paper no. 47, p. 66, pi. 10, figs. 1, 2 and 2a, 1906. 



io" For description of P. vancouverensis see Arnold, U. S. Geol. Surv., Prof, 

 paper no. 47, p. 140, pi. 52, figs. 3, 3a, 1906. 



108 For original description of P. peckhami see Geol. Surv. Calif., Palaeontology, 

 vol. 2, p. 59, pi. 16, fig. 19a, 1868. 



