80 TERTIARY AND QUATERNARY PECTENS OF CALIFORNIA. 



tions common to P. estrellanus. P. miguelensw may be the /•". catilliformis of 

 Conrad (Piic. R. R. Rept., Vol. V, Pt. II, p. 83, PI. IX, fig. 83, 1857), but his 

 description is so brief and his figure so poor tliat it is impossible to make an_ything 

 definite out of it. 



P. mUjnelenms is confined to the Miocene (probably lower horizon). 



The type is a slightly crushed specimen fi'om San Miguel Island. It is the 

 specimen figured, and is now in the collection of the University of California. 



Miocene. San Miguel Island (Univ. of Cal.); Santa Rosa Island (No. 12333, Cal. St. 

 Mill. Bureau); Santa Inez Valley, near Santa Barhai-a (J. H. Wilson); Santa Inez 

 Mountains, near Santa Barbara, Santa Barbara County (Pac. R. R. Expedition). 



Pectbn (Lyropecten) perrixi n. sp. 

 PI. XIV, figs. 1 and \a; PI. XV, fig. 1. 



Description. — Shell averaging about 150 millimeters in altitude, somewhat 

 longer than high, inequivalve. equilateral, of medium thickness, ventricoso, and 

 with smooth margins; base regulaflj^ rounded; sides sloping and decidedly 

 concave above. Right valve nearly flat, with about 23 unequal, narrow, moi'e 

 or less rounded, and often prominently imbricated, radiating ribs, which are 

 sometimes dichotomous; interspaces unequal, narrow, and occasional^ ornamented 

 by a small auxiliary rililet; surface sculptured by fine incremental lamellse 

 which are much more prominent in some specimens than in others; hinge line 

 about one-half length of disk; ears about e(iual in length; anterior ear wide, 

 ornamented by concentric incremental sculpture; byssal notch wide and deep; 

 posterior ear ornamented by several prominent, more or less imbricated radiating 

 ridges, and concentric sculpture. Left valve quite prominently ventricose, other- 

 wise similar to the right, except that the ribs seem to vary even more in 

 I'elative size and spacing; anterior ear lacking notch, otherwise ears similar to 

 those of the right valve. 



Dimenxionx. — Alt. 150 mm.; long, (restored) 16o mm.; hinge line (restored) 

 80 mm.; diameter 55 mm. 



This is a most variable species, there being no two specimens sculptured 

 in exactly the same manner in a series of over fifty specimens examined. The 

 convexity of the valves is almost constant, the variable factors being the number 

 and relative importance of the intercalary ribs, and the prominence of the 

 incremental sculpture. 



The geologic range of P. perrini is from the lower to the middle (?) 

 Miocene. It is found associated with Pecten 7nagiioUa, and other characteristic 

 lower Miocene fossils between Mori'o and Toro ci'eeks, San Luis Obispo County, 

 while at Roblar, in the same county, it is found with P. discus, a species found 

 usually in the Santa Margarita formation. 



The type, an imperfect specimen, of which both valves are figured, is from 

 the lower Miocene between Morro and Toro creeks, San Luis Obispo County, 



