134 TERTIARY AND QUATERNARY PECTENS OF CALIFORNIA. 



showing' through the valve. Shell •suliorbiciilar, barriiiy the auricles, which are wide 

 and prominent. Lower [or right] valve flattened, 0.1 inch (2.5 nuUinieters) smaller 

 than the upper one; sculpture of fine, close, equal, concentric ridges, sharply defined and 

 separated liy narrow non-canaliculated grooves. Valves covered with a fine velvety 

 epidermis, ashy and very finely radiately striate. Surface of the valve, except for 

 the ridges, smootli. Anterior auricle long, prominent, with a deep sinus. Posterior 

 auricle small: l)oth with strong elevated lines of growth, which rise into scales on 

 the 8 or 9 fine ribs with which tiie antei'ior auricle is furnished. Hinge line straight, 

 smooth. Inside of the valve polished, furnished with 21 rounded, radiating ribs, with 

 traces of others intercalated near the margin; nodulous or swollen at the more prom- 

 inent ridges of growth and at the margin. 



"Upper [or left] valve similar, inside; anteiior auricle shorter, not so deeplj' 

 sinuated. Valve more convex than the undei' one, and a little larger. Dorsal areas 

 finely granulate. Umbo smooth; half way toward the margin the stria- of increase 

 become more conspicuous, and about 3.5 pseudoribs radiate toward the margin. 

 These are formed by the elevation of the concentric lines of growth like rutlles, in 

 such a way that the edge of one tinting of the ruffle overhangs the beginning of the 

 next, and so on. These are very fragile, and when broken awaj' show the nearly 

 smooth surface of the valve underneath, without any true rib at all. Faint ribs are 

 intercalated between the pseudoribs toward the margin." 



Dimensions. — Alt. 19.5 mm.; long. 19.5 mm.; hinge line 9 mm.; dium. 6 mm.; 



iimbonal angle 100-. 



This beautiful little deep-sea form is distinguishable from the other small 

 Pectinidx of a like habitat by its internal lira^ and the lack of radiating sculpture 

 on the right valve. Its nearest allied species in the Pacific coast waters is 

 P. (iavidsiini^ which, so far as known, is confined to the deep waters west of 

 certain parts of Alaska. 



P. ala.shiiisis is found living, and is also preserved in some of the Pleistocene 

 deposits of Alaska and Vancouver Island. No record has as yet been made of 

 it in the fossil state in any of the Pleistocene deposits of California. (vSee 

 P. 'rivers!, pp. iy<)-127.) 



RANOE. 



Living. Bering Sea to Panama Bay, usually in deep water (Dall). 

 Pleistocene. Various points in Alaska (Dall); Point Holmes, Comox, Vancouver 

 Island (W. Harvey; C. F. Newcombe; Dall). 



RECENT PECTEXK 



[Those known only in the recent faunn of the west coast.] 



Pecten (Pecten) excavatus Anton. 

 PI. XLVI, figs. 1, 1((, and 1/-. 



1835. Pertrn dentatiis ft B. Sowerby, Proc. Zool. Soc, 1835, p. 109; Thes. Conch., vol. 1, pt. 1, 

 1842, p. 49, pi. 15, figs. 105-106; not Pecten deiiiatus J. Sowerby, Min. Conch. Gt. Brit., 

 vol. 6, 1829, p. 143, tab. 574, fig. 1. 



1839. Pecten excamtns Anton, Verzeichniss der Conchylien, 1839, p. 19, No. 710 (erroneously 

 reported from C'liiiia). — S-cr^ r,A-oJ 



