70 TERTIARY AND QUATERNARY PECTENS OF CALIFORNIA 



comparatively small. Right valve with about 20 subequal, promi.ient, rounded, 

 somewhat imbricated ribs, which increase gradually in numl)er ))y division and 

 intercalation as the shell grows; interspaces somewhat narrower than ribs and often 

 containing one or two thread-like intercalaries; ears as in /'. hastatus var. hencius 

 except less imbricated, and the posterior relatively larger. Left valve similar in 

 evei'v respect to right. 



Dimensions.— A\t. 46 mm.; long. 39 mm.; diameter 13 mm. ; umbonal angle 82°. 



This variety is cliaracterized by the nearly uniform size of its ribs and inter- 

 spaces. The shell has a tendency to contract somewhat upon reaching an altitude 

 of about 35 or 40 millimeters. /'. var. hyde! is closely allied to the typical P. 

 sesjMensis, but may usually be distinguished by its more nearly equal ribs, which 

 are generally more strongly imbricated. 



In a tributary of Little Sespe Creek, Ventura County, Mr. Eldridge found P. 

 var. /iiy(/e/ associated with Scute/la fairhanl'si, Ostrea sp., Area sp., and Bahtnus. 

 Near the Torrey wells, Ventura County, the same gentleman found it with Mytiliis 

 mathexosonii^ and Ostrea (aff.) titan. In the Ojai Valley it occurs with Pecten 

 magnolia and Ohione n. sp. (large; coarse sculpture). 



The type specimen is from Lynch's Mountain, Monterey County, where it was 

 found associated in the lower Miocene (Vaqueros sandstone) with Txirritella hoff- 

 niannJ, Pecten estrellaiius., and other species characteristic of this horizon. It is 

 now in the collection of Delos Arnold. Named in honor of Prof. James M. Hyde, 

 of the University of Oregon. 



RANGE. 



Miocene (lower). Lynch's Mountain, Monterey County (Arnold); vicinity of Little 

 Sespe Creek, Torrey oil wells, and Ojai Valley, Ventura County (Eldridge). 



Pecten (Lyropecten) bowersi n. sp. 



PI. XII, lifjs. 1 and 2; PI. XIII, fi;;:^. 1 and hi. 



1856. ? Peclen veradamis Conrad, Pac. K. R. Kept., vol. 5, p. 329, pi. 8, fig. 77. 



I)eserijjtion.—':^\\el\ averaging about 150 millimeters in altitude and length, 

 inequivalve, equilateral, rather thick, ventricose, and with smooth margins; base 

 regularlv rounded; sides sloping, the anterior ones slightly concave upward. 

 Right valve considerably less ventricose than left, the surface of the disk being 

 almost flat until an altitude of 50 or 60 millimeters is reached, when it begins to 

 be more or less convex; surface ornamented with about 18 subequal, prominent, 

 rounded ribs, which, with the interspaces, are obsoletely radiately striate and 

 crossed by tine wavy incremental lines; the ribs tend to become smaller toward 

 the sides of the disk, there being a varying number of riblets near the sides in 

 difl'erent specimens; interspaces subequal, round bottomed, about as wide as the 

 ribs, and sometimes containing an auxiliary riblet; hinge line about three-fifths 

 length of shell; ears about equal in length, anterior ear divided into two nearly 

 equal parts by a line radiating from the apex, the part above the dividing line 

 being ornamented by 3 or 4 radiating ribs and concentric lines while the lower 

 part (byssal area) is ornamented by imbricating incremental lines which are convex 



