PLIOCENE PECTENS. 107 



'wholo surface is covered by several more or less prominent concentric undu- 

 lations and ininierous tine, sqiuirish, imbricated, raised riliiets; hinge line a little 

 more than one-half the length of the disk; anterior ear about one and two-thirds 

 lengtli of posterior, ornamented by about 12 radiating riblets and numerous tine, 

 sharp, imbricating, incremental lines; byssal notch about one-fourth length of ear 

 in depth; posterior ear much smallei- than anterior, l>ut sculptured in a similar 

 manner. Left valve with about 7 broad, flat, round-cornered ridges of uneciual 

 size, which are separated by interspaces of unequal width, there being 3 or 5 

 prominent ribs, between each pair of which is a smaller one; the surface of this 

 valve is sculptured similarly to that of the right, except that the concentric 

 undulations on the ribs become more or less prominent nodes toward the apex 

 of the shell; ears similar to those of the right valve, <>xcept that the anterior 

 one has a simple arcuate end and no notch. 



Dimensions. — Alt. i;5(i mm.: long. 14:5 mm.: hinge line 75 nun.; diameter 

 50 nun. 



This species is quite similar \.o and is no doubt the precursor of 7*. suhnixlnxus. 

 from which it ditfers Ijy attaining a larger size and having fewer and ln-oader 

 ribs. Like the living form, it is quite variable as regards the number and 

 rugosity of its riijs. 



The only locality from which this magnificent species has so far ))een reported 

 is Cerros Island, off the coast of Lower California, where it is associated with 

 P. cvrriisensls, P. leenntci, Ostiva veafc/iit\ and O. ccrrosensis in beds of probable 

 Pliocene age. Doctor Cooper confused one of the large Miocene Pectens {P. 

 iiuuinoVm) with this sp(^cies when he reported it from the Pliocene of Ojai 

 Valley, Ventura County. (See Seventh Ann. Rept. Cal. St. Min., 18SS, p. 246.) 



The specimen Kgured is the t^'pe, which is now in the collection of the 

 University of California. 



RANGE. 



Pliocene. Cerros Island, off Lower California (Dr. J. A. Veatch). 



Pecten (Chlamts) b.\ktschi n. sp. 

 PI. XLI, fig. 3. 



DescrijJtion. — Adult shell averaging about (iO millimeters in altitude, somewhat 

 shorter than high, convex, slightly inequilateral; base regularly rounded; margins 

 smooth. Valves with about 40 prominent (more or less unequal) narrow thread- 

 like ritis, ornamented on top by numerous short imbricating spines; interspaces 

 deep, narrow, and channeled; lateral areas rather narrow, perpendicular to disk, 

 and slightly concave. Ears similar to those of P. islandiciix. 



Dimensions. — Alt 62 mm.; lat. 50 mm.; diameter 28 mm. 



This species, of which only two or three rather poorly preserved specimens 

 are known, is quite closely related to P. opuntla, but is readily distinguishable 

 by its much larger size when adult, lack of concentric constriction in the later 

 stages of growth, and relatively shorter disk. 



P. haiischl \» found in beds of probable lower Pliocene age at Crescent City, 

 Cal.. where it is associated with Terehratalia near hcm^jlillU Dall, Phacoldes 



