OLIGOCENE PEOTKNS. 55 



from /'. IxJhis hx its fewor rib.s (11 instead of 14) and ndatively smaller size 

 when adult. 



/'. xaiirtiv.ci'iiZ'iisix is so far known only from lieds whicii appear to be tran- 

 sitional from the Oligocene to the lower Miocene. At locality No. 111(L. 8. J. V. 

 Geol. Survey) on Twobar Creek, one-fourth mile above its junction with 8an 

 Lorenzo Rivei', Santa Cruz County, the tj'pe was found associated in a soft sand- 

 .stone with the followinj;' species; P,-ct( n hniiiDrr! n. sp., Cytli(/r(i {>■/'.) rt-.spertina, 

 Ti'ifonJuiK sp. No. 1, <'orhi(l<( {]) sp.. Voldia {<■/.) hiqjres.m, Niicida n. sp. (lai'ge, 

 with coarse sculpture). Led<( sp. B. and C, Cidaris {'.) spines. (MlliMa sp., Tellma 

 {AiK/idus) sp.. Ciird'niiii n. sp.. near i-oajwri^ Trrcdn sp.. Cliione ief.) iii(dheirxoni. 

 One mile southeast of CowelFs asphaltum quarry (locality 30), near Santa Cruz. 

 P. Kanctsecritzensii^ is associated with /'. peckhmnl, Nucuhi sp.. I'lmcoidcx sp., and 

 Chioiw sp. 



The type, a beautifully preserved mold of a left valve, is no« in the collection 

 of the department of geology. Stanford University. A small cobblestone con- 

 taining two right and two left valves of /'. ■•<iiiicfa'cri(sc/ix/.-: was found by Miss 

 L. J. F. Hecox, of Santa Cruz, as float in Beai- Creek, about 2 miles from the 

 type locality. One of these right valves is figured and serves as a cotype. 



Oligocene-Miocene. Twoliar Creek and Bear Creek. Santa Cruz County (Arnold; 

 Hecox). 



Pecten (Chlamys) bkanneki n. sp. 



PI. Ill, ligs. 9, 10, and 11. 



DeKcr'ipf'xin. — Adult shell averaging about so millimeters in altitude, higher 

 than long, ecpiivalve. slightly convex, and equilateral, except for ears; sides only 

 slightly concave abo\e; base n^gularly rounded lielow. Jtight valve with from '.io 

 to '1^1 prominent, nari'ow. more or less scaly or spiny rilis, which in the adults 

 are sometimes medially sulcated or dichotomous; interspaces generally much 

 l)roader than the ribs, channeled and usually containing a sj)iny or scaly inter- 

 calary rib; whole surface sculptured by imbricating incremental lines, often also 

 by microscopic reticulations; hinge line about two-thirds length of disk; anterior 

 ear much pi'oduced and sculptured by 6 to 10 imbricated ridges, which are separated 

 by equally wide reticulated interspaces; byssal notch profound; posterior ear 

 about three-fifths length of anterior, and sculptured similarly. Left \alve similar 

 to right. 



Dimensidnx. — Alt. 65 nmi.; long. .58 nun.; hinge line -to nun.: diameter 14 

 nun.; umbonal angle 83^. 



Lhis species varies considerably in the degree of importance of the minor 

 sculpture, such as reticulation, imbrication, and size of the sulcations and 

 intercalaries. Although unquestionably allied to the ('hhimys group, it has larger 

 posterior ears than other species of the group that have come under the writer's 

 notice. P. branneri resembles P. idandicus in size, outline, and general sculpture, 

 but is distinguishable by having only about one-half as many I'ibs and much larger 

 posterior ears. 



