UNIVERSITY OF TORONTO LIBRARY purchased for the Geology Collection from the VARSITY PALAEONTOLOGY FUND Digitized by the Internet Archive in 2010 with funding from University of Toronto http://www.archive.org/details/faunaofsanpablogOOclar a’ ° ’ =) ey i | wire 6 iA Tr ' # ! UNIVERSITY OF CALIFORNIA PUBLICATIONS BULLETIN OF THE DEPARTMENT OF GEOLOGY | Vol. 8, No. 22, pp. 385-572, pls. 42-71 Issued August 30, 1915 “ = KE T4/ FAUNA OF THE SAN PABLO GROUP OF C20 MIDDLE CALIFORNIA BRUCE L. CLARK CONTENTS Introduction and Acknowledgments .... BETS OIUCAUTUOWACW 2 eco-<-2-< Spy <2-.---eeeee 448 Pecten (Pecteni?) cierboensis) m. Spe <-qceccce-ceeee-aseeee ee 449 Pecten (Plagioctenium?) crassiradiatus, 0. Sp. -<-c-ccccecesc-eeccesseeseeeeeeeeeee 450 Pecten (Pecten) raymondi, n. sp. ....-.... se atcseccedenecssvons$ coau-5e cS eeee eee 450 Pecten ((Chlamys)) pabloensis!(Comrad) fee cece ee 452 Pecten (Pallinm)) tholwaryi, ms spy 2cccceceee-cceceeeee sees 454 Peeten (@Pallinm:)) olwalya, ms Sys 492 2S DRS, TORN OUTS TST CU 0 a eee ee ae ee pe ee 493 PEMTesr ia Har V SE Si eM U NTS OTe SPs aeeen dean stan sore esa ea deena tone ar teoteneeearaaeenenenenceaassos 494 RG HiRe BOC OMUS DUWAlGI,. Te (SPs. (occa aseecancecce sn aees waco cn eat eos oes eaee ana ear ae ee reeeeteasnee 494 388 University of California Publications in Geology [ Vou. 8 PAGE G@hrysodomus Cereboensis; M1. Spe -ecsnerenaecnnaneere nce ene ces eres p anc enm neem eae ane ee nena 495 @hrrySodomius Cia DOC Sisy stl Speers axeee manent eee see eer eee re ee 495 Clr SOd OMS pa DLO eS IS ine cement en ne eee ener 496 Supp Morven ery ermal Gri Srey he eee nee 497 Trophon carisaensis Anderson 497 Trophon gracilis Perry var. pabloemsis, n. VaY. ---.------------------0-----eeeeeeeo-oee 498 Alaoya)evoser (GMM RET, Th, (5]0, cece ec ece eect cece esecceennce sce suoe cocee emecsedepecceesuesaseeace 498 Ebro Wome atywy, SOAs uecte hS (epesesee eee eee ee eee 499 Trophon ponderosum Gabb 499 Trophon ponderosum Gabb var. pabloensis, n. var.? -..--.----------- 500 Murex: ((Ocinebra)) \dallitjem: (spy ec ence cee en so cease 501 Miumnex: ((Oeimebra)) packard, We Spe reseecenenessces cera ese ea rae ee eee 501 Murex ((Ocinebra)) selbyensis, UW. Sp). sxa--2:-.cee--enees-o=eeeceestes cone eee eee 502 G@amcelllarval PablOensisy ms Spe cencse ae mne ener ere ee mere e en na 503 Murris ATK eNSiS 5 00S (SY): acca n can eece seme nee oem ame 504 Wescription ot WO ca CUS) ease eee seceeemeee ere een eee eee tee re ee ee 505 INTRODUCTION AND ACKNOWLEDGMENTS The San Pablo Group, as described in this paper, represents what originally was defined by Dr. J. C. Merriam as the San Pablo forma- tion or beds equivalent thereto. The preliminary work on the paper was begun in the summer of 1910. The writer has been fortunate in having at his disposal the large collections from the San Pablo Group made by the classes in Palaeontology of the University of California Summer Sessions of 1910, 1911, and 1912. These collections were in part made under his direct supervision and in practically every ease he has had first-hand knowledge of the field localities. In presenting the paper it is realized that many problems have been left unsolved and that much remains to be known concerning the details of the fauna of the San Pablo Group of Middle California. It is hoped that the data given here will form a basis for a more com- plete study of the fauna of this horizon in the near future. The writer wishes especially to express his acknowledgement to Dr. J. C. Merriam, under whose direction the work was begun. . aan Es be Plas es) Le ee _ see ” Pecten crassicardo Conrad . B = 5 % i : Saat x =2 x a me oe Res 4 i : a ‘“ Pecten holwayi, n. [SFOS crocs ener rere eee eon - ia 5 y: = 5 aS = GO: ieee) La as aes os * c % x Pecten pabloensis Conrad ; cs = Andg': oe a eRe ak ae Se ar % + . E : Pecten raymondi, n, sp. .... - = a I a ea 8 ee x re ere ot oon eS eke 7 Pecten weaveri, n. sp. SE gisae, eens ens a 7 eee ese SSS) co * - es oe a ee ees agora aa a =. a aed se tad era a Pinna alamedensis Yates . i = ae Z a x a ee ee ey ee Peas Pa, nt z mean ? e ws - Pitaria bebri, n, sp, — * cee: gee a ene eee rk ee ee > eens ee Sy Pitaria stalderi, n. sp. x a > are a4 5 S = - = a + a her = era al ce 5 a ie i c i z i - — Sanguinolaria nuttallii Conrad es a 2 ewes =e we iho Mn RS ana eet Ve See as en eed rc Sanguinolaria? n, sp. aA Ge NO Lt ¢ eee be] agi MERC, Gi See oe LE ee x Saxidomus nuttallii Conrad ese sees ee a A She X) Par ee st ye ree pee ae SK ria, - . Schizothaerus nuttallii Conrad = is : 8 SS ae SS SRE ees. wae et Se EP a en we De . F ; : Schizothaerus pajaroanus Conrad s 5 _ eae ae ae. ee tee ew eeter eS _ i Siligna lucida Conrad . ao sinees x 5. "i on eee yl ae oe a i SCE Meh n a 1 pt eae x Nai ae Solen perrini, 0. 8p. 3 a va, x se x as eta x ze % = oe — —— “a anh pen osat ws Ww Spisula abscissa Gabb .. a a ~< = 5 = SS £2 ee | ee eee ae Ostrea titan Conrad . Panope generosa Gould . ag ee . oo eee TRS Sie Lee eee BE Sa. Paphia staminea Conrad . : Wi Pert se Oe lee Ad = Pecten bilineatus, 2. Sp. ... a see — ad —- — a poe =p = = - <~ E pes Pecten CcierbOeMSiS, ND. SP. ....--------c-n-ceneceesneeernccerenseeeersee on aa - xX = > ee : es = et Tae Pe eS Oe 4 ie x « Pecten crassicardo ONT US SE te eee ee - nate see ooo a = ee Ps a - Seen ante me . — Pocton Owe ya, : Wisi Ba gerstece nicer araeestuesaresicoventy sorereancoe cree neee - a Wer $5. ee x x = . ose =a ease, x ~ — Postar. Wweavert,. Vy Bpageeteececcaceceee tpt engee tans Kae tee seers new naee = a x He ame ners wee é RASS oe otal ee a Pinna alamedensis Yates ..........-...---sscccssccerssseeceseorenceeese sone acco acco oose = oe cose ait se aoe ay anes! ED ee ae ez acne wave oe - Pitaria DeLTI, TM. BP. ssetteecqc-eqnsnso-neevorasannvennorsecarnscopeaevde ay ae ase > es x ease = wee ones sone sai ane ees x pe ae) ie a, aS Reus ae" = oad Pitaria stalderi, n. sp. ........ haa sips ee op avec ede ae Seo whe eae aan x eS - oe ote sere =ene Fae sc= aoe sees — ied oo pond =n) — a at! <= ee tess ance one =e - “ a oe ~ Sanguinolaria nuttallii Conrad «0... -scscssssesncceccnssseneee secs hwo -+r/ Saaey eee x seen wham eee Se ier a a a sate x 2 con ce Se woul eae nace fen Sanguinolaria? n. sp. ... <= Se ooh wore a z ~ cess mam “a S/vana in Punve = 7 = ee xidomus nuttallii Conrad eae ee ae x x =, ee x = > =e - x se, + - - Si haerus nuttallii Conrad . x = x a - x er a oo someth y) ete nits Se = x x chizothaerus pajaroanus Conrad x - wee - oo wee cee - a > ne x Siliqua lucida ONT Bye Baers cs Socomacokcsccuntrbucsecctocecicecsscocens aa eal aad ae oa oeee soot oe x sree aoe nee a o-- = i =are Pond 5 WU GN EATN 5 a0 PD 2 ere egies acces Somer eras vote poessage acs room oe, pas — ose ns os a sce a ote rp pa = : B QD BCIBRH CATA 2e ster ie eien rae sterecesceeee eee _ Bh, +; a ai” $e cos mete x Me. eS Pe x x Mec bazse pas oe Ee eae | BID BTIEI CONNEC ieee crctenrnoertacmcesteerecenscteertete-teaeysce ee ec - ee Ce en Re a ey Se ee ee a) RS x teas ha ppisula Srinite eatilliformis Conrad ...............----.«--.--- ee ~ i ae x : _ — = an Sine ah one wis a, a a a — — — — ae eee Jee ne x ote os _ Spisula, cf. falcata Gould |e az = hee me a5 sda aaeeeey tas dene tee aad oe = an ee Chrysodomus pabloensis, 0. Sp. -....--.-.-scecececeseeseeserceeeeee anil Xi ate X .... Se aes oe Se ae ee er sats ee. oeks 2. “eaan,” Seek ae ee ee ee CRP BO COMO, BPs. sasaisscascascecuacanconlespaaeeee eaten euareeereteemeentae Sains) ge : 52 3 7. Lee 7 : : Set tee Dentalium, sp.? be Syee inne wna Seat Raga LA eA | Per REE Es teat eS Le See x Korba soe | ae eens. \ - Vane : fot Epitonium borealis Gould .......csccsessececcssssssseescscccesecesaeeee & x ee i z Ma - xe Oe a Popes » aes Ficus, ef. st ifordensi LOLG 252 ee eee eee na py . x ae et eee ie ae Ses ey ae eae aie a Bes a —- mbt pred Sica eian eves oe sone cove Hemifusus dalli, n. sp. Murex (Ocinebra) dalli, n. BPs foscevevstcsrenncstnshishocaraentertae ri ‘ a c a ; Murex (Ocinebra) PAckardinm BPs es enschede x x oS 3 tg i ; Murex (Ocinebra) selbyensis, n, 1) Urner x x f ER : pias ee ‘ ene Nassa pabloensis, n. sp. x 7 a ; 4 Ps i . ; Natica (Euspira) kirkensis, n. sp. x eres he Soe = * eae ae * Natica (Neverita) arnoldi, n, sp. = cos ry ;; } ba % Natica (Neverita) recluziana Petit ....ccccccccccccsece-o0.---- ' ee ie ass BURNS & es Natica (Neverita) pabloensis, n. Sp. -.....ccs..ccsscsssecesereee Si ee = wea fimttseets feena, levensah a emia Me - ats & Sree Flat 7 Mie ; i, ; Olivella pedroana Conrad ............:ccsscecsesssseesecceesesseseeeee 2 gf koe ae eee Boe ess ht Ee ee) a d,s ne Ie eee ne es np ts ee ; PBIB YUE MABE Wn acces coasts SacassscascaecesSsccbcbesxctyssssecks x <5 ees Pa, hy we ae OE x SaehDorn aoe 3 os nyse x tw = ; Trophon carisaensis Anderson -...ecccc.cccececcececeecsesecoeeeeee EP Cree oe A Rey ee Bate) oS a a a a Oe ee > pa aR ee ae + be . Drophorm Mieke Orson wun 8D is csctesaccccss cesta oecteciacs ce ia PS x Pe eas ih ies iw snsyeicamaye taens) Oncor aves ans I 3 << ; a AS aH wey aa Trophon gracilis var. pabloensis, n. Var, ...-.-..-.cs0---+--- x op ih ae oe io gs % Lee | SNR ieee ieee oe DrOpnON. AWHONN ADs iasdeactoe stack aks a eo Pe Le EY Le Se AG ch MM 2 Oy PP rae See a ce oo a PS ae 1915 | Clark: Fauna of the San Pablo Group 401 Spisula abscissa, Tivela diabloensis, Chrysodomus pabloensis, Murex selbyensis. Division B.—The most fossiliferous portion of division B is in the sandstones just above the band of shale already described. Over forty species were obtained from this zone, a large number of which have never been found in division A or in the lower portion of any other section of the San Pablo Group. The species that appear to be char- ‘acteristic of the zone and which are found in more than one section are Astrodapsis twmidus, Acila conradi, Cyrena californica, Macoma pab- loensis, Macoma andersoni, Mytilus perrini, Mya dickersoni, Pinna alamedensis, Pecten pabloensis, Pecten bilineatus, Tivela gabbi, Natica (Neverita) arnoldi and Trophon carisaensis. Astrodapsis twmidus is found in the beds above the shale in great abundance, and in some places the coarser sandstones are made up almost entirely of the individuals of this species. The Pecten beds deseribed by Dr. Newberry in the Pacific Railroad Reports are found in this horizon and the types of Pecten pabloensis Conrad, Pecten bilineatus, n.sp., Pecten holwayi, n.sp., were obtained from them. Pecten crassicardo is also found at this locality (Univ. Calif. Loe. 1632). Other localities are nos. 1613, 1614, and 1615. The fauna found below the shale member in the upper San Pablo is not essentially different from that above with the exception of a few species, ineluding Diplodonta parilis, Sanguinolaria nuttalli, Tellina salmonea and Trophon lawsoni. A noteworthy fact in connection with the discussion of the fauna of division B is that in at least two zones we have estuarine or brackish- water deposits, as is evidenced by the presence in great abundance of the forms of Cyrena (Corbicula) and Mya, associated with genera which at the present time are found living under either estuarine or marine conditions. The first horizon of estuarine or brackish-water deposits is the shale member. In this the species Cyrena (Corbicula) californica was found, together with leaf impressions. The other zone is near the top of the group in medium fine sandstones. At locality 1617 in this zone certain layers are composed almost entirely of the shells of Cyrena (Corbicula) californica and Mya dickerson. 402 University of California Publications in Geology [ VoL. 8 Tue NortH Sipe or Mount Drasro STRATIGRAPHY AND LITHOLOGY The San Pablo Group on the north side of Mount Diablo has a maximum thickness of about six hundred feet and a minimum thick- ness of about four hundred feet. The deposits, especially in the lower part of the section, may be classed as distinctly those of a strand line, being largely composed of coarse conglomerates and cross-bedded sandstones. East of Kirker Creek, there is a well-marked irregular contact within and about three hundred feet above the base of the group, and at several localities the trunks of silicified trees were found standing at right angles to the contact. No difference in dip and strike was obtained between the beds above and below the unconformity. The San Pablo above the unconformity in this section is formed largely of layers of bright blue sandstone and pearLeray, tuffaceous shale. Near the top several small lenses of conglomerate were observed. There is considerable tuffaceous material throughout the group, and in the upper part of the section thin layers of white tuff are quite common. In this area the group unconformably overlies the Monterey Group and is in turn overlain unconformably by the Pinole Tuft. The un- conformity between the Monterey and San Pablo in this loeality is of such a character as would seem to represent a fairly notable hiatus. Briefly, the evidence is as follows: 1. At certain localities there is a difference in strike and dip between the two groups. 2. An irregular contaet between the two was found at several places. 3. The basal beds of the group rest on different members of the Monterey as one follows the line of strike. 4. Borers of the pholadid type were found in the Monterey rock alone the contact for a distance of over three miles. 5. Well-rounded pebbles lithologically identical with the tuffaceous sandstone and shale of the Monterey below, are found in the basal conglomerate. FAUNA The fauna obtained from this section of the San Pablo Group was deseribed by the writer?? in a former paper. A few changes have been made in the faunal list and a few species have been added to it. 22 Clark, Bruce L., op. cit. 1915] Clark: Fauna of the San Pablo Group 403 Scutella gabbii is found at the base of the section. The most com- mon species found with Scutella gabbii or in the same horizon are Dosinia merriami, Modiolus gabbi, Ostrea bourgeoisii, Pecten crassi- cardo, Siliqua lucida, Spisula abscissa, Spisula albaria, Spisula catilli- formis, Cerithiopsis turneri and Natica (Euspira) kirkensis. The beds of the upper portion of the lower San Pablo contain a number of species that do not appear in the basal beds, the most com- mon of which are Mytilus coalingensis, n. var.?, Sanguinolaria alata, Calyptraea diabloensis and Littorina remondit. Calyptraea diabloensis, Mytilus coalingensis n. var ? and Sanguinolaria alata appear to be characteristic of this horizon; all oceur also on the south side of the Mount Diablo anticline associated with Astrodapsis tumidus subsp. cierboensis and Scutella pabloensis, together with an assemblage of species that is very similar to that on the north side of the mountain. Thus the two lower minor faunal zones of division A of the Bay Section are also recognized on the north side of Mount Diablo. The fauna of the upper San Pablo in this area is to be correlated with that of division B of the San Pablo Bay section. The character- istic species are Astrodapsis whitneyi, Cyrena (Corbicula) californica, and Trophon carisaensis. Tere, as in the San Pablo Bay section, the ereat abundance of Cyrena (Corbicula) californica in the upper part of the group indicates brackish-water or estuarine conditions. 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Wiad aa Sora Aa act a2 peRimoH U][[e}JNU snULOpIxeg pags i Bie ON a Ne kee aie 2 ag) ae ein ioe Mae ks ce ON Bee Neca oe car eae a qqey vyV[V BIIepoUTNSURY So ee eee Mee ace! MRC eng ca eae Sg-aS AR hgegs ark area aa ea a a ids voprpepoyg perme) BE A, oe es ace ee SNe ae Mat eae etre Ae i oe es ~ udp vqydjnosmnue, saproovy *VadodANUTA 1915] GPOG TFOS OFOG EE0G PE8T E68T T68T OG8T ESPI 90h GOP 2OT OOT 29 09 6S 406 University of California Publications in Geology [ Vou. 8 SoutrH Siwe or Mount D1asio STRATIGRAPHY AND LITHOLOGY The San Pablo Group on the south side of the Mount Diablo anticline has a maximum thickness of about twenty-six hundred feet, as contrasted with the six hundred feet of strata on the north side. Here, as is also true of the group north of the mountain, the beds vary as one follows them along the strike, and only a generalized statement of the section can be given. All of the formations on the south side of the mountain dip very steeply; in some places the beds are vertical, and at points along the strike they are even overturned. In the vicinity of Shell Ridge to the east of the town of Walnut Creek, the Mount Diablo anticline has been overturned toward the southwest and on the south side the San Pablo dips to the north at an angle of about 60°, resting on the Pinole Tuff, which is younger, and is in turn overlain by the Monterey, which is older. The general strike of the beds on the south side of the moun- tain is about North 50° West. Lithology.—The lower fifteen hundred feet of the San Pablo, as measured in the vicinity of Tassajero and Sycamore creeks, are chiefly sandstones. At the base of the section Tassajero Creek cuts through a heavy conglomerate which cannot be followed for any great distance either to the north or to the south. Above these basal con- olomerates are about seven hundred and fifty to eight hundred feet of alternating layers of coarse, fossiliferous sandstones, massive, non- fossiliferous sandstones and thin layers of conglomerate. On the north side of Tassajero Creek, and stratigraphically about seven hundred and fifty feet from the base of the group, there is a thin band of ereenish-yellow shale. There is an irregular contact between this shale and the coarse, conglomeratice sandstone aboye. Above the sand- stone are about eight hundred feet of medium fine, shaly, gray-brown sandstone. Above the medium fine, shaly, gray-brown sandstone just men- tioned, and about fifteen hundred and fifty feet above the base, is the most persistent shale member of the group; its thickness is about twenty feet and it is continuous for over ten miles. In some loealities it contains many impressions of leaves and rushes, suggesting estuarine, brackish, or fresh-water origin. No shells were found, but a study of the fauna above and below the shale strongly suggests that it comes 1915] Clark: Fauna of the San Pablo Group 407 at the same horizon as the big shale member in the upper part of the group as described in the San Pablo Bay section. In the vicinity of Sycamore Canon, on the south side of the Black Hills, the leaf-bearing shale mentioned above is overlain by a heavy fossiliferous conglomerate, the pebbles of which are composed mostly of andesite. In Sycamore Canon a well-marked, irregular contact was found between the shale and the conglomerate, with borers of the pholadid type extending from the conglomerate into the shale. This unconformity was noted at two different localities over a mile apart. The beds above the shale member just described are even more variable than in the lower part of the section, and consist of alternating layers of pearl-gray shale and blue sandstones, together with lenticular beds of conglomerate. In the vicinity of Tassajero Creek, there is a zone of irregularly bedded conglomerate and sandstone about two hundred feet strati- graphically below the top of the group. The observed thickness of this zone is over fifty feet at several localities. The materials grade rapidly along the strike from sandstone to conglomerate and vice versa. The zone was traced for a distance of over fifteen miles, southeastward from Walnut Creek, but its maximum extension in that direction was not determined. No fossils were found in this zone. The pebbles in the conglomerate are noticeably round and some of them are two to three inches or more in diameter. In the field, they were referred to as the river conglomerates. On Railroad Ranch, about three miles northeast of the town of Danville and about one mile due south of Wall Point, there is a heavy, well-rounded, non-fossiliferous conglomerate, approximately in the same stratigraphic position as the conglomerate in the vicinity of Tassajero Creek. Lying beneath this is a pearl-gray shale containing an abundance of leaf impressions. At one locality just below the reservoir on the Mount Diablo road, a well-marked irregular contact appears between the conglomerate and the shale. Two miles southeast of the town of Walnut Creek and southwest of Shell Ridge (Concord sheet) there is a non-fossiliferous conglom- erate about one hundred and fifty feet below the top of the San Pablo, which at one locality is nearly fifty feet thick, but which rapidly thins out along the strike. This is very much like that seen in the region of Tassajero Creek and south of Wail Point, and probably represents the same zone. 408 University of California Publications in Geology [Vou. 8 In general, the deposits of a large part of the San Pablo in this section may be classed as shallow-water deposits, in part of marine, and in part of estuarine origin. Several unconformities within the eroup probably indicate emergence and land conditions of short dura- tion at several times during the epoch. Relation to Monterey Growp.—The Monterey Group cannot every- where be easily separated from the San Pablo, as the beds immediately below and above the contact are quite similar. An irregular contact was located by W. Kew, R. C. Stoner and J. H. Ruckman of the Sum- mer Session field class of 1911 on the south side of the Black Hills near Wall Point. This contact has been taken as the line of division between the two groups. Along this contact bore-holes of the pholadid type were found. A good fauna was not obtained from the upper beds of the Monterey in this vicinity, but between two hundred and three hundred feet below the contact are the coarse, gray sandstones of the Seutella breweriana beds, which contain a typical fauna of that horizon. Relation to Pinole Tuff and Orindan.—The San Pablo Group on the south side of Mount Diablo is overlain unconformably in places by the Pinole Tuff and elsewhere by the Orindan. In the vicinity of the town of Walnut Creek the Pinole Tuff is about two hundred feet thick; it gradually thins out to the south, finally disappearing, and in the vicinity of Tassajero Creek, is replaced by the Orindan which rests directly upon the San Pablo. DETAILED SECTION OF THE SAN PABLO GROUP ON THE SouTH SIDE OF Mount DIABLO AS MEASURED IN THE VICINITY OF TASSAJERO CREEK Orindan Formation. Fresh-water beds. (Uncomformity ) San Pablo Group, FEET Shaly sandstone 150 Leaf-bearing shale 10 Hard, bluish sandstone and conglomerate; (zone of ‘‘river con- glomerate’’) 50 (Irregular contact) Leaf-bearing shale 20 Medium fine sandstone with shaly sandstone toward top 720 Conglomerate containing Astrodapsis tumidus 15 (Irregular contact) Leaf-bearing shale 20 Medium fine sandstone and bands of sandy shale, with Astrodapsis whitneyi, A. tumidus, Pinna alamedensis, Trophon lawsoni, ete. 270 EXCHINODERMATA. Astrodapsis tumidus subsp. cierboensis Kew Astrodapsis tumidus Rémond Astrodapsis whitneyi Rémond Scutella pabloensis Kew: ----..----<--c-csssecss-cscceccceeeee-sanenens Scutella gabbii Rémond .........2..22.2.-cseessceseeeeeeeeee CRUSTACEA. Balanus, sp.? PELECYPODA. Area trilineata Conrad .. Cardium corbis Martyn Cardium quadrigenarium Conrad Chione diabloensis, n. sp. Chione pabloensis, n. sp. Cyrena (Corbicula) ealifornica Gabb . Diplodonta orbella Gould Dosinia arnoldi, n. sp. Dosinia merriami var, occidentalis, n. var Glyeimeris coalingensis Arnold Glycimeris septentrionalis Midd. - Macoma andersoni, n. sp. acoma diabloensis, n. sp. = acoma nasuta Conrad ... > acoma pabloensis, n. sp. Macoma secta Conrad Macoma, ef, yoldiformis (00) ieee en eee eee eRe Se Macrocallista neweombiana Cpr. Mactra trampasensis Packard .... Metis alta Conrad Modiolus eapax Conrad Modiolus direetus Dall Modiolus gabbi, n. 8p. . Modiolus merriami, n, Sp. . Mulinia densata Conrad ya (Platydon) eancellatus Conrad ya dickersoni, n, sp. Mya (Cryptomya) ovalis Conrad Mytilus coalingensis Arnold, n. var.? Mytilus perrini, n. sp. Mytilus, sp, indt. Ostrea bourgeoisii Rémond . Ostrea titan Conrad .......... Panope generosa Gould Paphia staminea Conrad .....0.ccs Peeten erassicardo Conrad . Pecten raymondi, n. sp. Petricola pabloensis, n. sp. Phacoides richthofeni Gabb Pholas, sp, indt. 22.0... Pinna alamedensis Yates Sanguinolaria alata Gabb Sanguinolaria nuttallii Conrad Saxidomus nutallii Conrad Schizothaerus nuttallii Conrad ......... Solen perrini, n. sp. Solen sicareus Gould . Spisula abscissa Gabb .. Spisula albaria Conrad Spisula catilliformis Conrad Quisnin nt falnatc Cinwla 746 749 x x Ea pipe’: BE: hes My = x one x ina x aene x JNAL 772 LIST 913 1474 1477 1478 1479 1485 1488 x x KKK 1490 1491 1495 1496 1499 1501 1504 1514 1518 1520 1936 1937 1938 1940 1942 1943 1944 1945 1946 1947 1948 1950 1952 1958 1954 1955 1958 1960 1961 - x x SS x x x x x x et ae tees x x} oY os x x x x x Mulinia densata Conrad . ibloensis Packard ............ Mya (Platydon) cancellatus Conrad Mya dickersoni, n. sp. peeereeeereeces Conrad Mytilus coalingensis Arnold, n. var.? My Mytilus, sp. indt. ...... Mya (Cryptomya) ovalis tilus perrini, n. sp. ...... ee : Ostrea bourgeoisii Rémond Ostrea titan Conrad ...... Panope generosa Gould .... on Sas eae x Paphia staminea Conrad ............-.----ce-escseeceseseceerenrecsenee 3 Pecten crassicardo Conrad .............::.cccsceceseesceeneceeeeeees Pectan: TRYAMOMG AB, coke gh conc ceca n wee cecerdm vee reve rsaceaeen x Petricola pabloensis, 0. Sp. ....----.c0c-cscssesescerenssecceceeessceee Phacoides richthofeni Gabb Pholas Pinna ¢ BPs QUO bs pocrecseconne amedensis Yates Sanguinolaria alata Gabb ........ Sanguinolaria nuttallii Conrad Saxidomus nutallii Conrad.. Schizothaerus nuttallii Conrad Solen perrini, n. sp. ...... Solen sicareus Gould . Spisula abscissa Gabb Spisula albaria Conrad .. Spisula catilliformis Conrad ....... Spisula, cf. faleata Gould ...........+.--- Tellina englishi, n. sp. Tellina hannibali, n. sp. Frenette ea cckestendoaraeeenataance Tellina pabloensis, n. sp. Tivela diabloensis, n. Sp. ....--.----- 7 Tivela gabbi, n. sp. Venus martini, n. sp. ... cic tose cas Zirphaea dentata Gabb STROPODA. Acmea, sp. indt. Astralium raymondi, n. sp. Bittium trampasensis, n. sp. Phesscb bi anchecsverence Calliostoma bicarinatum, n. sp. Calliostoma splendens Cpr. var. diabloensis, n. var... Calyptraea diabloensis, n. sp. -..-...-.. Calyptraea filosa Gabb ta Gabb Calyptraea martini, n. sp. - Calyptraea inorr Chrysodomus buwaldi, n. sp. . Chrysodomus iabloensis, N. SP. ......cccceceececeeteneeeeee Chrysodomus imperialis Dall Crepidula onyx Sowerby ........---.-.-- Crepidula pabloensis, n. sp. .. Ficus, sp. indt. Nassa pabloensis, n. sp. . Natica (Euspira) diabloensis, n. sp. Natica (Huspira) kirkensis, n. sp. Natica (Neverita) arnoldi, n. sp. Natica (Neverita) pabloensis, n. sp. Tegula (Chlorostoma) nashi, n. sp. Trophon carisaensis Anderson .. Trophon lawsoni, n. sp. ‘Lrophon ponderosum Gabb Trophon ponderosum Gabb var. diabloensis, n. var... x 4 1915] Clark: Fauna of the San Pablo Group 409 FEET Fine-grained sandstone 230 Beds made up almost entirely of shells of Mulinia densata 3 Shaly sandstone; contains Astrodapsis tumidus, subsp. cierboensis, and Astrodapsis pabloensis 100 Medium-grained, partially laminated sandstone 360 Conglomerate to pebbly sandstone 15 Light, massive, fossiliferous sandstone, containing Astrodapsis tumidus subsp. cierboensis, Scutella pabloensis, Mytilus coalingensis, n. var.? 250 Massive, medium-grained sandstone 72 Coarse sandstone and bands of fine conglomerate 100 Massive sandstone and heavy conglomerates 50 Coarse, soft sandstone 40) Coarse-grained sandstones with minor bands of conglomerate; Scutella gabbii zone 88 Conglomerate, pebbles small and rounded 6 2624 (Unconformity ?) Monterey Group. Secutella breweriana zone, mostly coarse conglomeratie sandstone. FAUNA The two major faunal zones found in divisions A and B, of the San Pablo Bay section are also recognizable in the San Pablo group on the south side of Mount Diablo. In the section in the vicinity of Tassajero Creek there appears to be no marked lithologiec change or stratigraphic break between the two zones, but there is a very marked difference between the faunas below and above a line which lies about 1400 feet above the base. Below this line Astrodapsis tumidus subsp. cierboensis, Scutella pabloensis, Mytilus coalingensis, n. var.? Spisula abscissa, Chrysodomus pabloensis and Calyptraea diabloensis are some of the most common forms. Above this line and separated from the lower fauna by only a few feet, Astrodapsis tumidus, Astrodapsis whitneyi, Pinna alamedensis, Mulinia densata, Trophon carisaensis are found in abundance. The beds, in which the lower fauna is found, are here designated as division A and those containing the upper fauna as division B. Division A—The fauna of division A is divisible into two minor zones, which are correlated with the two lower minor faunal zones of division A of the San Pablo Bay section. Here also the division is made on the basis of the sea-urchins. At the base of the group Scutella gabbii is found; stratigraphically only a little above this, Scutella gabbii disappears and Astrodapsis tumidus subsp. cierboensis 410 University of California Publications in Geology [ VoL. 8 appears. This species is found through a large part of division A.. The third minor faunal zone deseribed from division A of the San Pablo Bay section has not been recognized in any other section. The species associated with Astrodapsis tumidus, subsp. cierboensis both here and in the San Pablo Bay section, believed to be characteristic of division A, are Scutella pabloensis, Mytilus coalingensis Arnold, n. var.?, Spisula abscissa, Tivela diabloensis, Chrysodomus pabloensis. One of the most common species found in this zone and one which is believed to be at least locally characteristic of it, is Mytilus coalingensis, n. var? It oceurs with an assemblage of species very similar to that with which it is found on the north side of the mountain. Some of these species are Macrocallista newcombiana, Macoma nasuta, Ostrea bourgeoisii, Paphia staminea, Pecten crassicardo, Pecten raymond, Saridomus nuttalli, Schizothaerus nuttallii, and Calyptraea diablo- ensis. Division B.—From the 200 to 300 feet of sandstones just beneath the lowest and most persistent leaf-bearing shale of the Sycamore and Tassajero Creek sections, a very good fauna was obtained, including two species of sea-urchins, Astrodapsis whitneyi and Astrodapsis tumidus, and many mollusks, Some of the common mollusks are Chione pabloensis, Cryptomya ovalis, Dosinia arnoldi, Dosinia mer- riami var. occidentalis, Macoma secta, Macoma nasuta, Macoma ander- soni, Modiolus gabbi, Modiolus directus, Mulinia densata, Pecten raymondi, Pecten crassicardo, Pinna alamedensis, Venus martini, Astralium raymondi, Natica (Neverita) pabloensis, Cancellaria pab- loensis, Trophon carisaensis, and Trophon lawsom. Mulinia densata makes its first appearance in these lower sandstones of division B, a fact worthy of especial note. This species has not been found in the lower part of any section of the San Pablo group in this part of the state. One bed two or three feet thick in these sandstones is made up almost entirely of the shells of this species, and the layer is per- sistent for a number of miles along the strike. The typical Astrodapsis whitneyi was not found in the beds just above the lowest shale member of the Tassajero or Sycamore Canon sections. The fauna found above this shale, though not large, in- cludes a number of species that have not been found below the shale. Of these Tivela gabbi and Nassa pabloensis may prove to be char- acteristic of the upper part of the group. In the Walnut Creek section on the west side of Shell Ridge there was found at one horizon a fairly large fauna. In this vicinity (Shell Ridge) the lower part of division B is composed of fairly coarse sand- ——_ 1915 | Clark: Fauna of the San Pablo Group 411 stones about 100 feet in thickness. This is overlain by a fine, white, tuffaceous shale, which is approximately seventy-five feet thick. Many leaf impressions are contained in the shale, and, toward the top, Cyrena californica, Mytilus perrini and Macoma pabloensis were found, sug- gesting that these deposits were either of brackish-water or estuarine origin. Above the shale is about two hundred feet of medium-grained, blue sandstones containing Astrodapsis whitneyi, associated with a very meagre fauna. Above the Astrodapsis whitneyi beds is a horizon of conglomerate, followed by massive gray sandstones and shaly sand- stones. Some of the most important fossil localities in the sandstones and conglomerates are 1942, 1947, 1948 and 1950. The most common species are Astrodapsis tumidus, Glycimeris coalingensis, Tivela gabbi and Mulinia densata. Some of the species in this zone that have not been found associated with Astrodapsis whitneyi, are Chione diabloen- sis, Macoma diabloensis, Tivela gabbi, Astralium raymondi, Calliostoma bicarinatum, Crepidula pabloensis and Nassa pabloensis. Some of the species in the Astrodapsis whitneyi zone, that have not been found as- sociated with the fauna mentioned above, are Astrodapsis whitney, Venus martini, Chione pabloensis, Dosinia merriami var. occidentalis, Tellina englishi, Cancellaria pabloensis and Trophon lawsont. There are good reasons for believing that the two minor faunal zones just described are also represented in the San Pablo Bay section. The assemblage of species in the most fossiliferous zone above the shale is very similar to that in the beds just above the Astrodapsis whitney zone of Shell Ridge. Tivela gabbi is present with a number of other species which have not been found associated with Astrodapsis whitneyi in the Mount Diablo section, but are found in the horizon above. The evidence for the correlation of the beds below the shale of the Bay Section with the Astrodapsis whitneyi zone of the Mount Diablo section is not so good. Astrodapsis whitneyt has not been found in that section, but the species Zrophon lawsoni, which has been found only in the Astrodapsis whitneyi zone on the south side of Mount Diablo, is present. In the Shell Ridge section the beds above the so-called river con- elomerates have not yielded many fossils, but farther to the south, in the region of Pine Cafion, a few species that may prove to belong to a minor faunal zone were collected near the top of the series. These are Astrodapsis tumidus large variety, Mytilus merriami and Trophon ponderosum var. pabloensis. The meagreness of the fauna from these 412 University of California Publications in Geology [ Vou. 8 beds makes it unsafe to generalize as to its distinctness. The localities from which this fauna was obtained are nos. 104, 118, and 1499. In general, division B of the San Pablo group on the south side of the Mount Diablo anticline presents three minor faunal zones. The faunas of the two lower zones, though similar, each contains a number of species not common to the other. These two zones are probably also represented in the San Pablo Bay section. In both sections there is a change in the character of the deposits along the line of the division of the zones. The third minor faunal zone, which so far has yielded only a meagre fauna, has not been certainly recognized outside of the section on the south side of Mount Diablo. Rocky RipGe A very interesting section of the San Pablo Group is seen on the south side of Roeky Ridge near the southeast corner of the Concord quadrangle. Here the thickness of the group is roughly estimated to be twenty-four hundred feet. STRATIGRAPHY AND LITHOLOGY Relation of San Pablo to Monterey Group.—The beds of the upper Monterey (Secutella breweriana zone) outcrop along the main crest of the ridge, where the species Scutella breweriana is found in abundance. The lower Monterey of this section has been faulted away and the coarse gray sandstones of the Scutella breweriana zone rest with a fault contact against the Orindan, which belongs to the Las Trampas Ridge section just to the north. The upper Monterey is hithologically similar to that seen on the south side of the Mount Diablo anticline and in the vicinity of the town of Walnut Creek. Above the coarse sandstones of the Seutella breweriana zone are about five hundred feet of medium fine, buff to yellow-brown and gray sand- stone in which is found a fauna typical of that in the fine sandstones occupying the same stratigraphic position on San Pablo Bay. Above the fine sandstones of the Monterey comes a series of coarse, massive layers of gray sandstone referable to the San Pablo and similar to the sandstones which characterize the lower San Pablo everywhere in this general region. The beds of both the San Pablo and Monterey Groups have prac- tically the same strike and dip throughout and so far as could be 1915] Clark: Fauna of the San Pablo Group 413 determined, the coarse, basal sandstones of the one grade downward into the medium fine sandstones of the other. Here again is a section in which no structural break has been found separating the San Pablo from the upper Monterey. Lithology.—The coarse, massive, non-fossiliferous sandstones of the basal San Pablo outcrop as jutting ledges along the high, nearly perpendicular canon walls. These sandstones are followed above by a series of fine and coarse sandstones, with several interbedded layers of fine conglomerate, which yielded fossils at two levels. A noteworthy feature of the San Pablo in this area is the presence of small lenticular beds of limestone near the middle of the group; two outcrops were found, both approximately at the same stratigraphic position. At one locality near the south end of Section 35, T 18, R 2 W, Mount Diablo base line, there is an outcrop of the limestone which is less than a quarter of a mile in length, and from a maximum thickness of eight feet it thins rapidly in both directions. The lme- stone grades downward into a muddy shale and sandstone and is over- lain by a considerable thickness of fine gravel. No difference in dip or strike of the beds above and below the lens could be detected. Some of the limestone is pure white and of a very fine, porcelaneous texture, fracturing conchoidally like flint, and some of it is more impure and of a darker color. No shells were found, but the impressions of leaves and rushes are very abundant. The other limestone locality is near the southwest corner of Section 5, T 2S, R 1 W, Mount Diablo base line, about one and a half miles southeast of the first locality. The question arises—Under what conditions were the beds of this character deposited? The presence of great quantities of dicotyledon- ous leaves and rushes shows conclusively that the limestones are not of typical marine origin. These limestones closely resemble those of fresh-water lake deposits, but it is not certain that they could not be formed under estuarine conditions. Limestones lithologically almost identical with those found in the San Pablo occur in the overlying Orindan in this same section. That these upper limestones are of lacustral origin is shown by the fresh-water shells which they contain. The beds above the limestone lenses in the San Pablo are mostly medium fine sandstones with occasional subordinate layers of shale similar to the leaf-bearing shale seen in the section on the south side of the Mount Diablo anticline. 414 University of California Publications in Geology [ Vou. 8 In this region, the Orindan rests directly on the San Pablo, the Pinole Tuff being absent. FAUNA The fauna found below the limestone on Rocky Ridge is to be cor- related with that of division A of the San Pablo Bay section and of the Mount Diablo section. Scutella gabbii and Astrodapsis tumidus subsp. cierboensis have not been found here, but in the section on Las Trampas Ridge, about a mile to the north, these two species occur in their proper stratigraphic sequence. On Rocky Ridge the following species were found below the limestone, and are believed to be characteristic of the lower San Pablo: Spisula abscissa, Mytilus coalingensis, n. var? and Ostrea bourgeoisit. Above the limestone, a fairly large fauna was obtained associated with Astrodapsis whitneyi. Some of these are Amiantis dalli, Cyrena californica, Mytilus trampasensis, Mytilus perrini, Macoma pabloensis, Mya dickersoni, Venus martini, Cancellaria pabloensis, Natica (Neverita) arnoldi, Trophon carisaensis. See localities 38, 39, 41 and 1224. Tick VALLEY SYNCLINE STRATIGRAPHY AND LITHOLOGY A good section of the San Pablo is found north of Las Trampas Ridge in the vicinity of Tice Valley, Contra Costa County, where it is a little over twenty-one hundred feet thick. The beds outcrop on both sides of a syneline, and are overlain by the Pinole Tuff and the Orindan Series. Relation of San Pablo to Monterey Growp.—In this section the San Pablo apparently grades downward into the Monterey, the beds of the two formations having the same dip and strike. The upper Monte- rey 1s composed of medium fine, yellow-brown sandstones, which are very much like those of the upper Monterey of the Rocky Ridge section. Iithology—On account of insufficient collecting localities in this area no attempt has been made to draw a definite line, corresponding to that between division A and B on the south side of Mount Diablo or on the bay. 1915 | Clark: Fauna of the San Pablo Group 415 The section is of interest because of its contrast to the Mount Diablo section which lies only a few miles to the east, these beds being made up almost entirely of sandstones, with little or no shale. Con- glomerates and leaf-bearing shales such as are common in the Mount Diablo section are lacking. The probable reason for the uniformity of these beds is that they were deposited farther away from the shore line. During much of San Pablo time the shore line was near the’ present site of Mount Diablo and these slight oscillations would have markedly affected the character of the depositions from time to time. A few miles to the west, in deeper water, the same changes in level would not have appreciably affected the uniform processes of sedi- mentation. The estuarine deposits of the San Pablo in the vicinity of Mount Diablo were undoubtedly formed in close connection with the shore line. The beds in the lower four hundred feet of this section consist ot fairly hard, coarse, fossiliferous sandstone, alternating with medium coarse massive sandstones. They are lithologically similar to the basal beds of the series on San Pablo Bay. In ascending order above the coarse sandstones are about six hundred feet of medium fine to medium coarse, fairly homogeneous sandstones; seven hundred feet consist of fairly coarse, gray sandstones, some layers of which are fossiliferous; about 300 feet of fine, dark brown to gray sandstones; and about 75 feet of coarse, tuffaceous sandstone. The San Pablo is overlain by the Pinole Tuff and the Orindan series. FAUNA Scutella gabbui was found at the base of the section. A little above the base, Astrodapsis tumidus, subsp. cierboensis was obtained, asso- ciated with Tivela diabloensis. About one thousand feet above the base, Astrodapsis tumidus and Astrodapsis whitneyi were collected from a zone which at localities 1121 and 1127 yielded a fairly large fauna. An upper San Pablo fauna was obtained at locality 2529. Macoma andersoni, one of the common species at this locality, is thought to be characteristic of the zone above the Astrodapsis whitneyi beds on the south side of Mount Diablo, and this zone is supposed to be equivalent to the very fossiliferous horizon just above the shale in the bay section. 416 University of California Publications in Geology [ Vou. 8 OrHeER LOCALITIES Other localities in Contra Costa county from which fossils of San Pablo age listed in this paper were obtained are Las Trampas Ridge, Lafayette Ridge, and southwest of Danville. Las Trampas Ridge—las Trampas Ridge lies less than a mile east of and parallel to Rocky Ridge. The San Pablo outcrops on the south side of the ridge and dips to the southwest at an angle of 60° to 70°; it rests upon the Monterey with relations analagous to those observed on Rocky Ridge. The two major faunal zones of the San Pablo are recognized here. Scutella gabbii is found at the base of the group, and Astrodapsis twmidus, subsp. cierboensis and other characteristic lower San Pablo species occur at a slightly higher level. A very good upper San Pablo fauna was obtained near the top of the group at locality 1182. Lafayette Ridge.—A few localities including Nos. 145, 149, 1195, and 1197, are listed from Lafayette Ridge, which is practically a con- tinuation of the section on the north side of the Tice Valley synchne; the two major faunal zones are recognized here. Danville. Trampas Ridge a short distance southwest of Danville, but the section San Pablo outcrops occur on the north side of Las is obseure. ©. E. Weaver listed several species from one locality which the writer has also visited. A typical San Pablo fauna, cluding two new species of gasteropods, Tegula (Chlorostoma) trampasensis and Leptothyra danvillensis, was obtained here and is listed under loealities 1635 and 1636. COMPLETE LIST OF KNOWN SPECIES FROM THE SAN PABLO GROUP OF MIDDLE CALIFORNIA, WITH THEIR GEOLOGIC RANGE The following is a complete list of the species from the different sections described in this paper. The different zones in which the species occur are indicated in the columns. With the exception of the collections belonging to the University of California, the chief sources of information in regard to the species common to the San Pablo, Santa Margarita, Jacalitos and Etchegoin, have been Dr. J. P. Smith’s?? paper on the ‘““Geologie Range of Miocene Invertebrate Fossils of California’’ and the collections of the California Academy of Sciences in San Francisco. 23 Proe. Calif. Acad. Sci., 4th series, vol. 3, pp. 161-182. — cece ES x ; x cee ‘ds ‘u ‘sisuoorqed ouorgy ea a ech x - x oA ‘ds*u ‘sismao[qerp ouolyy) eee oe x a o == ere x aioe drreporg epronijed vuey) primo) wutwedestupenb wnrpie) Ecu 3 A FAUNAL LIST 88 ag 145 147 149 1182 1195 1196 1197 1199 1219 199) ,,.4 1225 1227 1231 1237 1239 1240 1245 1249 1251 1257 1259 1265 1270 1271 1278 1274 1275 1636 ECHINODERMATA. 4“ 122: Astrodapsis tumidus, subsp. cierboensis Kew x Astrodapsis tumidus Rémond ... a0 ss 25 7 ia cat (et, . So ee “ ee = aA = wane Ai cada, 7 eect Woes ee ee Oe EET Recerca ne Se Astrodapsis whitneyi Rémond . ‘ 2. =a 6 x 2 eS x % I ee teh NS Ge OM eit YT Nig be AES Fi ey eer ceo Scutella gabbii Rémond ............ceesesssecneessecnneens sesneereense ea ie eee I A Sm Sy Peed ae eee < aay = PELECYPODA. AMIANGAVGRUT MSBP: sasscectescssctcvesesecastecos x x =e) a) es es a ae get eh er ES pe PS it = Cardium quadrigenarium Conrad ae ais eee Se) So ee - a z Cyrena (Corbicula) californica Gabb By h ane x xP as AS = = as x Glycimeris septentrionalis Midd. ...... f x es ae ee x 22 eee A Se = ~ r as 2 aed <- Macoma andersoni, n. sp. r cecil whSeee ane Res 2s ee aren dle Oe wes tent tae “abies E 3 2 ee Macoma nasuta Conrad .... _ | ae “chee BP ats cad aaa SOM > ace ye at SUE CoA RRO BC ea I a Fe Nog See Macoma pabloensis, n. sp. x co Src oe ni cacer Y NESE RS 9¢ © la geek: A MlccR In cea Ins Uaioe 5 OE aA ee age oe ace = ee NE wave, eee Macoma secta Conrad ewe a et cers - Se ete 8.) iy te ce Sieg, oe se = x a3 : Hg Hal Mactra trampasensis Packard nes = | eae enc et, ew 3G Pane 4 Set | Maced “= ste * es) Pee - Metis alta Conrad Modiolus directus Conrad . Mulinia densata Conrad .. Mulinia densata var. A. .... Mulinia pabloensis Packard .. Mya dickersoni, n. sp. Mya (Cryptomya) ovalis Conrad x be. 5 2 tie x ‘ ce re ES nil aes Kees X weve eee . ’ wens Mytilus perrini, n. sp. x ee aoe ee a ek Xx Seas Mpp heen | sees, agent. te ‘ Peo ove “ : oer Mytilus trampasensis, n. sp. x ey F s £ - ade et en Kenia! aoe > AD aie x : . x Soa Ostrea bourgeoisii Rémond Sic) Ae a yd F aerogenes oe AS a 5 . . sf ok : Ostrea titan Conrad ss. a r e a es me 3 =P oA es “ oe . Paphia staminea Conrad Pecten crassicardo Conrad .. Pecten estrellanus Conrad . Pecten raymondi, n, sp. ........ Pecten pabloensis Conrad .... Pinna alamedensis Yates Pinna, sp. indt. A E 7 s 2 Ss 3 pees Cre is He . x a ee “ . anaty Bes es x dene esee Spisula abscissa Gabb ... a 4 ae hs wake ih tease ch 5 ada a (evs ote see Saxidomus nuttallii Conrad .. Schizothaerus nuttallii Conrad .. Siliqua lucida Conrad Solen perrini, n. sp. Spisula catilliformis Conrad Spisula albaria Conrad Z R 4 Le wRaapees x P . . cove - ; Tivela gabbi, n. sp. . 6 x x = yee ort ; oe xt Tivela diabloensis, n. sp. S75 aie . = okes ‘ a Lak §, ee Ve lcare) SEO syn, Yseore) aees ) ohaaee . one eee come . Wiemtibb mart lem prin BY): in sesencsceshcsctvesvattasocessetsteeecs- secession nuts dion PE X (aegis) [Gar (Gin oe oo see sees oP ate Le eS Sects GASTROPODA, Astralinm ray Ons) 0. Gp), csrenceecaccecsecessecceveteccoevssceeecc-ce Bittium trampasensis, n. sp. ... Bursa trampasensis, n, sp. ....... Calliostoma bicarinatum, n. sp. Calyptraea diabloensis, n. sp. . ofa i ie ne x x x a 1% 3 ap Vek és « x Calyptraea filosa Gabb ...... x x x P x ae x (4 Soo reese ee RHE , my aS Calyptraea inornata Gabb a 2 ps otk % eine Ts : oe se oa weiGa: nes Res ae Cancellaria pabloensis, n. sp. dere Ss a bs x Ss wee ae 7 aa = ? 2 Cerithiopsis bolingerensis, n. sp. ess Mi oe si - pte ey pi Wer Le wees tee r : im ; tenet rah 6 te Chrysodomus pabloensis, n. sp. .... Ve ie MRE etna ene Cae aes se Sane Seay \-F a ial egh “i i Columbella (Astyris), ef. tuberosa Cpr. mov ivese Teme Gabe) one cane ene) eee ecee | een 5 FAA ATO = Pe i i 2; Pate oe a os a . i Crepidula aduneca Sowerby ae co! Se i cre ee Prodan. eet. a : me Aut Se Crepidula onyx Sowerby bea ae ee BO fame eras ee Sig Ss 3 save |) (seen see ye 5 Gardinia reticulata Sowerby Meo as = yi ee Be ee ee = ab hrs nace me Leptothyra pabloensis, n. sp. .. Sty ESS ne. cs bce ee at eT we re cis eek : Murex (Ocinebra) dalli, n. sp. i i ee er > ew =; ins 8 oth See ake aes Nassa pabloensis, n. sp. ..... ace - x a eg SE nee Caer 4 9 We = ES eS A “ <= a - Natica (Euspira) kirkensis, n. sp. ... — = 3 Hs a a, > 4 Se Es Oe py ds Ad eo aout Natica (Neverita) arnoldi, n. sp. x x Ba bens x : : oe Mes ger 4 x x BES ees, Fare x x HF asec eee Be a ee eae ae Natica (Neverita) pabloensis, n. sp. x x - 2 eee Se tae Pe ee x SO EN, ocd Sicacae epee ep etesl oo ee En x «eee ie gs Mise oe x Tegula (Chlorostoma) danyillensis, n. sp. ans eee =r = ee Seip oe = eae OS oereip > corse Bina Bunce’: GSS) WCE a ye re Pawn fe fate per Ay Ae Thais lima Martyn 4 ee ES. we ees, eee ma Leela OS «| aes agape ee» 8 Saree. hy ch = 6 Cs, 2 Sa aa eae Trophon carisaensis Anderson ...............c:-ssesscecesereeeeeee x Se ae eee Ores Ba NA ee. ere Bt eh I ata ince ht cone pean eee 417 Clark: Fauna of the San Pablo Group 99209 N IaMory 1915] BUBIIaMaIq Bang, BUIRsIvyy Bury ojqed ueg TaMOrT olqeg urg aaddy soqRoee uloseyoyg RG KO KE Me SOC youyxXG Seed ss oe acsthoce ea paece Mans anercdencn oso acca ne cane rane ‘ds ‘u ‘stsuaotqed ouormy Gin Ia cerca carina ce char rac aaa hs nesscricaossatcnsrescns ‘ds u ‘sisuao[qetp ouoryy snes rineae tase reeetoretercnataeas on asen se sestra ct diepoig eproued veureyy Sr cshcerbesrnaoeste abaskarpcaecsendsnchancens peiuoy wniweuestupenb wnipaeg IR Sct oops cceea asin ac sasaea onan amennsoss(ercsrenes— UAJIVI STGL00 wNtTpreD pRIuoy vyvouTIT] Boly Bie Ape eaaratbasocces sere ecanep on astooce conan oeasecasnnnacnnsenrscseaot ‘ds au ‘t[ep stjuermiy Orn BRSESEECL Dar icra Scroct Jace oScR eoceepero ce acre eae oon se Yoo Ipeiu0d voy *VaOd ANNIE SMe ppeethcceeaeceoscroreotaaassacROacr eee yynourdo\ stsuojasnd ‘yo viqesod Gaec caae en ecioa re aaa nae aca =: sce as coos: orcas east asscna nascdennaehce aon q ‘ds ‘snuereg pe TEE EERE SEEASE ST D2> 60 -C0G OT HUE SO SSeS eS PEC CeCe etch ect Jc coc vy ‘ds ‘snuepeg ‘vaoVisoNy CERRY SEET ACROSS OEE Ocoee ORT eA re Ooo eacee ea Coco eee ceeo Seco sotaods ooaty, *VOZOAN, Rood) ScErRe Goatrcoerrcoceeote tcc epee MOY Stud} “TBA T1GqQes v[feynag GRO) OLE SaR RRO pcb Se crap org oee Re Enc Roce caer Pee SCE puowmay mqqes vijeynog Ce CERLERERC aS errr ong apebee sc care cere reece MOY StIsudo0[qed vifeynog fae | WN scor Sascha ocosacovocooas-ooo- nos oeeaohcacansasne>cscn cnesnawene qqey ipuowed sviioysy SERS EEECERCOA ES ReC ee eCot aoe area COLE aea puowsy téeuziyM stsdvposy Sarde el NS acerca eee aaa (‘IBA aSie]) puowgs, snpruny sisdepomsy peice fence se as cagc aoc ae aan oar rns ace ener puowoy snprun, stsdvporysy Se) bees creo aces MOY stsus0qierd "dsqns snpruny stsdeporysy G97 REET CEGL ES: SERED RSS PORE CRG EERE et CSCS CSE Moy snqye stsdeporysy ' “VLVWUAGONTHOOL 3 Es LSIT TVNOVA [Vot. 8 Geology Publications in va y of Californi werst Un 418 ama000N TOMO auoz VUBIIaMaIg Bag VIVsIV IY ByURg oqeg ues TOMO XSI KE KK) KT CCS ESSE SL es SS SC Re OE qed ues aeddgQ Xx yeep 80} u10s0yqo4y ( yoUNX panuryuog) quasay enn ee enn nn ene een nnn nnn nnn n nena nnn een n ne en anna nn wnn nnn ‘ds “UW ‘TuOsi100Ip BAW errr rere rrr rrr tert eee preyed sisuao[qud BLO I secren-thocees eenarPfc6- 6. col coc Seep cco SceSracraChEeEET “y CARA BIRSUAp LIMIT Saige erg epee ype Na eS ns peimoy Byesuop BrUIpNyy Bspaengar ees ener ia saa aa ‘dsu ‘1qqes snporpoy, Bescap ceeoeeas Tt Tl&’@ snyooarp snporpoyy Si Ge) oh igh ee Se a a peanoy xedeo snpotpoy, Spt permoy vy[e sey Iayuedrey stm1o0ftplod “Fo BULODR TY ~ PRIMO BPDOS BULODT I --ds ‘tu ‘sisuao[qed vuooryy Be eee ce ge rae ar ca a ae pRiuoy Buse BvIODRI Ger oer tC rca cao ‘ds ‘a ‘sisuaorqeip BvumooRyy SS apui cy anyon Te aie me aa ‘ds ‘u ‘tmosiapur vMmodR yy fea en goa aE eae aaa pieyovg sisuaseduedy) vrjoeyy Fa acne ea Id) BVUBIqUIODMOU (RI[OMOTYD) BIST][BI0LOB IY SE eg ane oe eee cee ee ay a ‘yput ‘ds epary passer re roo cess eae En *PPUN St[euorsjueydas stzswTAyy SS ae a ee Rr eT ploury stsuesurpeood staoudATY Pegi aiecssmareea ee ee ‘IBA ‘U ‘SI[R}UOPIOIO “ABA TUB ILIOUL BIUTSO(T Baa aris gar aree amie aa eases saeaaae es car i ae ‘ds‘u ‘turett0ur ~vIUIso(y Sener CS eae ee eae ‘ds‘u ‘tppoure ermtsog gate aee aaa aoe cern ae eae beng ae peiuoy sttaed eyuopordig Sa ahaa amigo SAreN Sen ae, plnoy eijeqro eyuopordiq ree aay Ae Se eer gaa as et qqey voruxozipes (B[natIqtoy) BuerApH “VdOdANTTE —LSIT IVNOVaA 419 Fauna of the San Pablo Group . . Clark 1915] aua00aN TaMO'TT eaoz vuvliaMerq Bleyag BLIVSIVY BURBS x xX Xx oqed UeS TaMorT oqed ureg aeddy cy iJ ° 2 =r oo i) n 4x wLosayoy = Se ee Jojuedirey vyd[nostnus, soptoovyd sas SIN erase ae eae cen Ona qqey toyoyyyots soploovyd co Sie gu csrecncer a coe aa ccacecas cc scnn aneeerenes boners aca peimoy snzr[nuue seproovgd Sera We nin eben mre mea Renan Ene Seen ae ‘ds‘u ‘ippeanqg Booted Gated 0m Se anosccnenc ocho cng eon anhere eho one sagan aaa oe ‘ds‘u ‘1eAvam 0}00q os Sigs enna go Sb oS ere ono S sa ogra eee ‘ds‘u ‘tpuowAvs 0104004 Bene). ioababanesncaescncea aan ae serenasn nernen nes ne ae peiuoy sisusoiqed woyooq Berea) UnAgRananania india sAnnr msn snRaanee nna asan" shee 185 Sposa sees ‘ds ‘u ‘tABMpOY 00400q ecg | p(bshscbaactnascesnanncns- espe Race ee nae nero Er ean RAE See peo, SNUB[erjse 10yeq On CCU Ge ay occ oceans das Sadao aa eG ‘ds ‘u ‘snyvoutiq 194007 Ske enc coe ar nenin anno gns anche ae snan seg acer cas Anse ‘ds ‘u ‘snyerpedisseid 010900 q SD ECE reels COSC Gy Oa cee ec aac PRIN OpABdIsseId 104007 Beast tasgancasanene enna ns csc shagasasarancan s1rassestnces-nrene® ‘ds ‘u ‘stsuo0qio1 uaqdaq x CECE eo CP Cae eo Co eae se eg bars Sec gooa pinoy vsoroues odourg nace S| esnartsbpsttcenacesocracseeanactasascscssnsnsessache saan nee peop vourmeys viydeg x Pace” (seearhrence rh nrkcnceeaschepeeentsarincnessensns sckceenchensnS:o acy peruoy ueyr} voa148O mS see ploury gsuenboes “iva peauoy vurztodsea vo1ysO are Do) issenonsensacc st cons erntaseenrethenhnerneersmennsceht seaneacoeee rojuediey BplIny Ba1}SO x Esa puoway Mmstoesmmoq vaijsO x ges ‘ds ‘u ‘srsuaseduvay (vyouosotyApy) supa x arnt ‘ds u ‘turmzed snityAyy x aoe --ds‘u ‘tuerem snp ayy x resi teaarcshe jreA‘u ‘ploury sisuesurtpeoo (eyouooo Ay) supa sap Gy gittaroctecncérarecasentenss-h>sontecao= prinoy snqyepooues (uopAzetq) BAT a Seng.) asechernnsns Ane Aeec re OS RnoCe SR ACE RCAC DAE peauop syeao (v{uoyddip) BAT *vaodAOU Tad Sy = og 8 8 5 (panuyuo9)—LSIT TVNOVA [ Vo. 8 Geology VONns UN icat ty of California Publ 20) Universi 42 aua200N TaMory PuUBIIaMeIg vas VULABSIVIL Byueg me 26 Ba Ws 2," o aura Sb Sk eK GF oiqed ureg asddy ay Sp ° ee S S n ulosayoyg x sess poise sare re “IBA “He ‘HINJRINSUB "IBA SISMOOTGRIP BLOAT, x Bese acre saarctaae casas oboe ecco as aeas ‘ds ‘a ‘stsuoorqurip Bloat, x eee eee een eee eee nee en nnn re enn en en ene nee n en nnneeeeennnenenne ‘ds ‘a ‘Tqqua BlOALT, Bats Sap) Wasss sc anesSca costae papers sprerensaroe Jojuediey BouOW[es BUTT, x Sang Sistas ctsracheg a ce ap tescrore cron sscatrceenaaeare ‘ds ‘u ‘stsuao,qetp 4 BUr|[O], x GT ag titatearseseseegmeanters rere reatr sete oe ge teens ‘ds‘u ‘tystpjsue vary[a., x SSReY oT (cgsamastscan pean aeernanesecestrasacerscstoange scree tea een ‘ds u ‘eqruuey eut[y[a,y, om Mi Saeeteecacsasar nag gear nceeonseetpconae cages a ae plnoy eyeopez “zo vnsidg are Son gesseurerascecbrsctercscazescrcosesee-coeesabccoeeso: peiuo0p siumsxos [Two epnsidg x So SSE Cece rere anti Sear permoy vriieqye epnsidg x CO DERE aes ae oc ar See fee qqey ussiosqe epnsidg a SR Acecerececeasastceses tach sos acacia Soe a cece cecccrecar seg ose ploy shervois wapog x a : ‘ds‘u ‘turaiod wapog cb x Sr Sasiae ata oaassstts Suanzcsonsteraerasnerororarecesc veneers permop eprony enbytg x co : ~ primo) snuvoreled snisevyyoztyag aos x peimoy Mm[eyyNU snasseyyoztyag oe x ; ~ pRIloy Mypeyynu snuroprxeg a ose Pewee ~ ads “; errepoumsueg a M0 8 Veit > pRImoy M[VyyNU BIeepouNsuRg x SECS accra a oe ae cee aga qqey vyeye eiepounsurg seek Boe Ger Eo eRe eS OECS ee i Core Se erce tT coSe ~ grds ‘sepoyg x pee eeseccaargen eae tae gees aarcet aie a seas ee ‘ds ‘u ‘t1ap[eqys BIIeyL x Fee star ree ercacenen sapien ee gee ees ge ‘ds u ‘tayaq Blaeqtg sah Son eg Bass cnacs casascerscstecn ao saeo ace noreccnc nena r pesca aeoie ns Pennastece areas cao g-ds ‘euurg x a) om a ae ik meh or A ae aes ark Fea oe a aa S0}e XA SISuopotmeR[e Buu *"VaodAOdTA B ® (panujuop)—LSTIT TVNOAWA Clark: Fauna of the San Pablo Group 1915] aua00aN IaMO'T au0g vurltaMmerq BILAINIS BPIBSIv]L ByURS oqed urg TaMO'T x x ore@d ueg aaddQ SoypBove & > S im ulosa x puyxg esse canncsner ares races anne ‘ds ‘snutoposdayy ~--ds ‘u ‘sisueoqiera snuoposAry(y --dsu ‘ippeang snmoposéay() ‘ds ‘u ‘sisua0opor WNIT LIA8:) ‘ds u ‘srsuerosurpoq stsdormyiaep --ds‘u ‘taourny stsdorggties ‘ds‘u ‘stsuoo[qed vrie[jaour) eds ‘u ‘turjaeut vevsyd Ape qqey eqyevusrour vovayddyep ~ qqey esoly vovaydéyep a See aac aan one Segnceencen ‘ds ‘u ‘stsuaorqeip vorayddpep Sareeseesr= “BAU ‘SISMOO|GRIP “IBA “d_) suapueTds vUOySOT][R: Barna ec sie mars ae a nan Sear ‘ds ‘euojsor[ep aagac Behan senna cecesecegersmeN er eocaonn eset ‘ds a ‘uinqeuriediq BMOJSOT[[eD ershsssdrsapcerccitscesnscseabccraroses scctes iN aseees cass estesere ‘ds ‘tu ‘eyeutied Bsing SCE eae occ at Sct a ‘ds ‘u ‘stsusopqed guni44tg age ae nag aaa As cen reeset nes ee aoa ame ‘ds ‘un141q SEeSSeenseste orecocheccroeessekatoaecensstesste-ooness ‘ds‘u ‘stsuosedmesy wn1441q Mesgaecnar a aa nase saa geae ne smcncna Scag ene Ce ‘ds‘a ‘tpuowdAer wnITRIISy Spaueeeeneneear nas passaranscas cess sooee nseoos oa ca-uae oe eee ocean oS CBE OB UTM eS er a ae ae gee ea gene cr a yds ‘noanqoy *yaodouLsyy) SStCeac conde oadec Sh coecoa bE See: esp CoE Raa Coc Ceece qqey vyejuep vevydarz Se poS oS etetaas) GoteR Son aeoaRSEEE SEC REESCESE EE ESoE ‘ds ‘u ‘gisuasotoured BIplOx SOR ESEL SE SoRE Cece caste Sn- ch ecco Rea e eco eeee eee e ET ‘dsm ‘turyreu snue~ *yaodxOaTa (panwjuw09)—LSTIT IVNOVA [ VoL. 8 in Geology ications Publ VW forn ity of Cali "SU Univer amua903 NT IaMO'T au0z BUBIIaMALG B]JaINIS BPAVSIV]L ByuReg ojqed ureg TaOMO'T aaddy o[qed ueg uloseqoyg qoulyxX --ds‘u ‘stsuoorqerp (vatdsng) vomenr ~-ds‘u ‘stsuoopqed esse yy > plnoy vorpuou esse Ny -cds‘u ‘stsuadqjos (Biqaurag) xeanyy --ds‘u ‘tpaveyord (eiqouig) xoeinyy Paka SEN ST AWA DEAS ‘ds ‘u ‘yep (erqeurg) xen Bpsoaua 7 apices 7 agen ae aby ae ca qqey tpuomeds BuL10yyvyT Say aan Peer ae SAD TEN Be ‘ds ‘u ‘stsuasanqs}qid evur10y4yry PT aise ke ER ea ‘ds‘u ‘stsuaorqed vadyqyoydory EOS sO Sa cre acca nano erasers ‘ds au ‘T][ep susngrumo yy Biase! tags hi ee ee aE AqIWMOG BYR[NITJeL BIUTpey wan ann en en ee nn ee nnn ee nen nnn enn n nnn n anne nena nana nnenmnn nanan nn 3:ds ‘snony Fate gaa cae ae ae ga plouly Sisuepsoszueys “Fo snonyT ees Stas SAE RAAT EER ie p[noy sipearoq wnrmozidg Gernot raver peu sid) esoreqny “fo (suAjsy) B[jequintoy Se ee ee Ce ‘ds ‘u ‘stsuasanqsyyid (stadysy) B[jequinpop Sear aorsaes vs Danae Tarra e eas te peauoy sdedurid vpnprdery Bene paar eae ee ‘ds ‘u ‘stsuao,qed ernprdery SSF eae een ogee x Sees eae Aqiamog xduo vnpidesp gag tence ake oar baer ee aaa AqiaMmog vounpe vpnptdesy eT eRe a ee ae ‘ds u ‘stsuao,qed snumoposéiyy Saag RY Ss at ar gig Goa ge lle’q stetsedmt snmoposdéiyqy Sra gs acs gee eae ‘ds ‘a ‘stsueo,qeip snuoposkiyp *yaod0uLsyy (papnjou09)—LSTT 'TVNOVA 423 Fauna of the San Pablo Group . Clark 1915] 919009 IaMO'T au0g BueiiomMoig Byjaynag BLIRS IVP Bue orqeg urg TaMOry oiqed ues aedd oy i] ° = os S n ulos9qo qounx gy quasay ae on Wate doen nvn decstoas Sone oeeSCaanEe Ss eaaas Scene acaecoeeeon a MTU DT LO (i *ya0dvHavog Tee een eae are pr eee ane neers area wc ea ‘ds ‘epjoqriainy, ‘ds ‘u ‘sisuayary Sting, ‘IBA ‘U ‘SISUIO[GeIp “IBA uMsOepuod uoydory, - qqey wnsorapuod uoqdory, ~-ds‘u ‘taosmer woydo.y, rv ‘u ‘stsueotqed ‘rea Atiog sttovis uoydory, --ds‘u ‘ruosiayotp woydorg, ~ M0Sieapuy sisueestrea uoydory, a iccare - uAqIVL BUI, Ste, ip WL AEA A ag ‘ds ‘u ‘sisuaoqiotd sreqy, srogeg coer eamngt Peer ee a ‘ds ‘u ‘tyseu (BUojso10[YD) B[Nsey, ear eec oan ‘ds ‘u ‘stsuaj[tAuep (emojso1ojyy) eB[nsey, eee eaea es acece aaa aera ae aca ‘ds ‘a ‘stsua][IAuep Bipeuoqdig Tee inate cane gat aca ee aa a peiuo0y vuavorped eppaat[o po ee aaa uae sega eee ‘ds ‘u ‘stsuao[qed (ej19AeN) BOTZRN pele rca eae aaa eae read Jyoq BURIZN[OAI (BIIBAAN) BOTYEN Gea dagroenc re ar ee rae ae rae gre ‘dst ‘tpjoure (Bjt1aA0N) BOTPBNy gees aes ie car anise gw Ba ‘ds ‘u ‘stsuoyaty (vardsng,) Boren *vdodOuLsV‘) (papnjouv0))—LSTT TVNOVA 424 University of California Publications in Geology [Vou. 8 SUMMARY OF FAUNAL LIST Species TO {o) aukitVe(s (spo NEI, cece eeenten cere ne ercne scheme cere ce cecb ee case Eooc aes ocse cee tae senchbceer ee coo sncomsosenerence 9 Pelecypoda 87 Gastropoda 63 B59 20 es 3 (Cory a th Che ee 3 Motallnumiberk of (Spe Cues ee eeececneane ernest Beer reper torrtected cet 165 Number of determinable molluscan species -.......-....-----------------ee-eeeeeneseeeeeeeeee 135 Number of Recent anolltuscam (Species sce sscrcescne sean ceenes ere nrs nee eereee eee nena 32 Percentage of Recent molluscan species to total of molluscan and echino- eK (SPOCLCS | soe acca care cen tee ee eee eee eo ea ee 21.2 Percentage of Recent molluscan species to total mollusean fauna -..... 23.5 Percentage of Recent gastropod species in determinable gastropod fauna 11 Number of echinoderm and mollusean species in Lower Major faunal V0) 5 = ae a OE a ar oer er err ee iat 76 Number of echinoderm and mollusean species in Upper Major faunal CAO NV ee Ee eo REE SEER ON SSP ret RE Sr emer merece aun nrenr sornccesosenseetet i 109 Number of species common to San Pablo and Seutella breweriana zone... 27 Number of species common to San Pablo and Santa Margarita of south. 38 Number of species common to San Pablo and Etchegoin-Purissima Hori- zon and including all Recent species found in the former which have not been! found) amithe lather) osama creer erences see 48 Number of species common to the San Pablo and the Lower Neocene. (Includes ‘‘Temblor, Vaqueros and Monterey,’’ not Scutella brewer- JANA -ZONO))s. -jcsccewsecvedacaceeeucsscessctoncuese soo oecseeeeeh eee eee aces ee nee 14 Number of new species and varieties described ...............----.-.----0-ssese00ecee-== 72 SUMMARY OF EVIDENCE FOR FAUNAL ZONES IN SAN PABLO GROUP Two major faunal zones are recognizable in every section described and in each are minor faunal zones. The minor faunal zones are estab- lished on the following evidence: (1) Scwtella gabbu is common in the lower San Pablo in nearly every section known. The species is not limited to the lower beds, however, as was formerly believed, for occasional specimens have been found at several localities well above the middle of the group. (2) Astrodapsis tumidus subsp. cierboensis first appears a little above the base and ranges well up toward the middle of the group; associated with it is Scutella pabloensis. (3) Astrodapsis tumidus and Astrodapsis whitney? are first found near the middle of the group. On the south side of Mount Diablo the latter 1915] Clark: Fauna of the San Pablo Group 425 appears to be restricted within a thickness of about two hundred and fifty feet of strata; and this part of the section is designated the Astro- dapsis whitneyi zone. Astrodapsis tumidus ranges well up toward the top of the group. (4) On the south side of the Mount Diablo anticline, the beds immediately above the Astredapsis whitneyi zone and above the lowest persistent shale of division B of that section, contain a few mollusean species which may prove to be characteristic of this horizon. At a few localities on the south side of Mount Diablo (in the upper beds of the San Pablo, above the so-called river conglomerates), a still higher minor faunal zone is indicated by the presence of a large variety of Astrodapsis tumidus. The two major faunal zones in the series are separable not only on the basis of the sea-urchins, but also on the basis of the molluscan fauna. There are some differences between the molluscan faunas in some of the minor faunal zones as has been shown in the deseription of the fauna from the south side of the Mount Diablo anticline; those differences, however, are not so great or well founded as those between the two major zones. The following species present in the lower zone have not been found in the upper zone, or in any other formation stratigraphically above the San Pablo. Those marked with an asterisk have not been found in more than one section. Scutella pabloensis Kew. Tivela diabloensis, n. sp. Astrodapsis tumidus *Tivela diabloensis var. angulatum, subsp. cierboensis Kew n. var. *Asterias remondi Gabb. *Bursa carinatus, n. sp. Dosinia merriami, n. sp. *Cerithiopsis turneri, n. sp. Mytilus coalingensis Arnold, *Columbella (Astyris) kirkensis, n. var? n. sp. Ostrea-bourgeoisii Rémond. Chrysodomus pabloensis, n. sp. *Pecten cierboensis, n. sp. *Fieus, ef. stanfordensis Arnold. *Pecten weaveri, n. sp. *Littorina remondii Gabb. *Pitaria behri, n. sp. *Murex selbyensis, n. sp. *Pitaria stalderi, n. sp. *Trophon gracilis Perry, Sanguinolaria alata Gabb. var. pabloensis, n. var. Spisula abscissa Gabb. *Trophon dickersoni, n. sp. The following species from the upper major faunal zone have not been found in the lower zone and have not been reported from any formation above the San Pablo group. Those marked with an asterisk have not been found in more than one section. 426 University of California Publications in Geology Astrodapsis tumidus Rémond. Astrodapsis whitneyi Rémond. *Acila conradi Meek. Amiantis dalli, n. sp. *Chione pabloensis, n. sp. *Chione diabloensis, n. sp. Cyrena (Corbicula) californica Gabb. Mytilus perrini, n. sp. Mytilus trampasensis, n. sp. Ostrea titan Conrad. Pecten bilineatus, n. sp. *Pecten holwayi, n. sp. Pecten pabloensis Conrad. Pinna alamedensis Yates. *Pinna, sp. indt. *Sanguinolaria? sp. *Tellina englishi, n. sp. *Tellina pabloensis, n. sp. Tivela gabbi, n. sp. Venus martini, n. sp. Astralium raymondi, n. sp. *Bittium pabloensis, n. sp. Bittium trampasensis, n. sp. Cerithium rodeoensis, n. sp. *Cerithiopsis bolingerensis, n. sp. [VoL. 8 Dosinia arnoldi, n. sp. Dosinia merriami var. occidentalis, n. var, Macoma diabloensis, n. sp. Macoma andersoni, n. sp. Mulinia densata Conrad var. A. Calliostoma bicarinatum, n. sp. Calliostoma splendens var. dia- bloensis, n. var. Caneellaria pabloensis, n. sp. *Chrysodomus buwaldi, n. sp. *Chrysodomus diabloensis, n. sp. *Leptothyra pabloensis, n. sp. *Littorina pittsburgensis, n. sp. Murex (Ocinebra) dalli, n. sp. Nassa pabloensis, n. sp. Natiea (Neverita) arnoldi, n. sp. *Tegula (Chlorostoma) danvillen- sis, nl. Sp. Tegula (Chlorostoma) nashi, n. sp. Trophon carisaensis Anderson. Trophon ponderosum Gabb var. diabloensis, n. var. Trophon lawsoni, n. sp. The lists show that the lower major faunal zone contains fewer characteristic species than the upper. In almost every section de- seribed, the collecting in the lower zone is not so good as in the upper. It would not be safe to conelude finally as to the distinetness of the two faunas, for more thorough collecting in the future may prove a greater range for some of the species now regarded as characteristie¢ of one or the other of the zones. The following species common in the upper and lower zones have not been found in beds younger than the San Pablo Group: Scutella gabbii Rémond. Modiolus gabbi, n. sp. Mulinia pabloensis Packard. Pecten crassicardo Conrad. Pecten raymondi, n. sp. Zirphaea dentata Gabb. Murex (Ocinebra) packardi, n. sp. Natica (Neverita) pabloensis, n. Sp. 1915] Clark: Fauna of the San Pablo Group 427 RELATION OF SAN PABLO FAUNA TO RECENT FAUNA A noticeable feature of the San Pablo fauna is the close genetic relationship of many of its extinct species to the Recent fauna of the Pacific Coast. Every such species is related to a form now living in the same geographical province as that in which the fauna of the San Pablo would be found if it were living at the present day. Below are lists of the extinct species and the Recent species to which they are obviously closely related. Extinet Acila conradi Meek. Amiantis dalli, n. sp. Chione diabloensis, n. sp. Chione pabloensis, n. sp. Macoma andersoni, n. sp. Macoma diabloensis, n. sp. Tellina englishi, n. sp. Tivela gabbi, n. sp. Tivela diabloensis, n. sp. Astralium raymondi, n. sp. Columbella (Astyris) kirkensis, n. Sp. Calliostoma splendens var. dia- bloensis, n. var. Leptothyra pabloensis, n. sp. Littorina pittsburgensis, n. sp. Murex (Ocinebra) dalli, n. sp. Murex (Ocinebra) selbyensis, n. sp. Natica (Euspira) kirkensis. Natica (Neverita) pabloensis. Tegula (Chlorostoma) nashi, n. sp. Recent Acila castrensis Hinds Amiantis callosa Conrad. Chione simillima Sowerby. Chione simillima Sowerby. Macoma indentata Cpr. Macoma nasuta Conrad. Tellina idaea Dall. Tivela stultorum Mawe. Tivela stultorum Mawe. Astralium undosa Wood. Columbella (Astyris) gausapata Gould. Calliostoma splendens Carpenter. Leptothyra carpenteriana Pillsbury Littorina planaxis Nuttall. Murex (Ocinebra lurida) Middendorf. Murex (Ocinebra lurida) Middendorf. Natica i Euspira) lewisi Gabb. Natica (Neverita) recluziana Petit. Tegula (Chlorostoma) aureatine- tum Forbes. TEMPERATURE CONDITIONS OF SAN PABLO SEA We may judge of the temperature of the waters of the San Pablo sea from the present geographical range of the Recent species in its fauna. With this as a criterion, the waters of that sea were of about the same temperature as the waters of the present coast between Point Conception and Santa Barbara. According to Philip P. Carpenter,”* the temperature of these waters is about the same as those of the 24‘*Mollusea of the West Coast of North America,’’ Brit. Assoc. Rep., p. 167, 1856. 428 University of California Publications in Geology [ Vou. 8 Mediterranean Sea, and should be classed as middle temperate. Twenty-nine Recent species are known from the San Pablo and of these eighteen range as far south as San Diego. We may conclude therefore that the fauna of the San Pablo lived under fairly warm temperate conditions. CORRELATION For the purpose of this paper the writer considers the Neocene section of California to be divisible into Lower, Middle, and Upper Neocene. The Lower Neocene as used here includes the ‘‘ Vaqueros,’’ ‘‘Temblor,’’ and ‘‘Monterey ;’’ the Middle Neocene includes the San Pablo Group (including the Santa Margarita of the southern part of the state); the Upper Neocene includes the Etchegoin, Purissima, Merced, Fernando, Wildeat, and the Pliocene deposits at San Diego and San Pedro. PREVIOUS CONTRIBUTIONS Before the position of the San Pablo in the marine Neocene section of California is discussed, the writer will briefly review the papers which contain data concerning the correlation of the San Pablo. No attempt was made by the early palaeontologists, Gabb, Conrad, Cooper and others, to divide the Upper and Middle Neocene of Cali- fornia into definite faunal zones. Even as late as 1895 little was known about the faunal zones in the Upper and Middle Neocene. G. H. Ashley,?° in a paper entitled, ‘‘The Neocene Stratigraphy of the Santa Cruz Mountains in California,’’ included all the Upper Neo- cene of that area in the Merced Series. The base of the series was believed to be close to the, border line between Miocene and Pliocene. Ashley recognized that in going from the bottom to the top of the Merced series there was a change in the fauna. The fauna from the base of the series was believed to be more closely related to the Miocene than to the Pliocene, and these lower beds were called transitional beds. On page 330, in speaking of these transition beds, he says: It would therefore seem that the lowest, or what might be called the Pecten beds, are more closely related to the Miocene, but a rapidly changing fauna soon gives the beds a Pliocene aspect which is maintained through most of the section, 25 Proce. Calif. Acad. Sci., 2nd series, vol. 5, pp. 273-365, 1895. 1915] Clark: Fauna of the San Pablo Group 429 Ashley did not separate the fauna of the transition beds from that of his typical Pliocene beds. That he believed his Merced series rep- resented the entire Upper and Middle Neocene is shown by the fol- lowing quotation from page 322 of the paper just cited: It seems possible that most of the beds from which the older Pliocene have been reported will be found to correspond to this series. Thus the fauna from Kirkers Pass and Green Valley, Contra Costa County, Santa Rosa and Russian River, Sonoma County, would suggest the presence of the Merced series. Dr. J. C. Merriam,** in a paper on the Neocene sea-urchins of California, appears to have been the first person to recognize two distinct faunal zones above what is here designated Lower Neocene. He points out that the. San Pablo is without doubt older than the Merced, the type section of which is just across the bay from that of the San Pablo. In 1903 Dr. W. H. Fairbanks?’ deseribed, under the name San Pablo, a formation in San Luis Obispo County, which he correctly re- garded as the equivalent of at least a part of the San Pablo of Mer- riam. The following year, however, he described these beds under the names Santa Margarita and Pismo formations, placing these in what he termed the San Pablo group. In 1904, H. L. Haehl and Dr. Ralph Arnold?* subdivided the Merced series of Ashley in the Santa Cruz Mountains into the Purisima formation below (5000 ft.), and Merced formation above (5000 ft.). The upper limit of the Purisima was placed in that part of the section regarded by them as corresponding to the base of the type Merced at Seven Mile Beach. From this time on there was considerable confusion as to whether or not the faunas of the Purisima and of the Merced in the Santa Cruz Mountains represented respectively the San Pablo and Merced as differentiated by Merriam. In 1905, Mr. F. M. Anderson?® published a paper entitled ‘‘A Stratigraphic Study in the Mount Diablo Range of California.’’ This was followed in 1908 by a paper entitled ‘‘Further Stratigraphic Study in the Mount Diablo Range of California.’’ In these papers 26 Bull. Dept. Geol. Univ. Calif., vol. 2, no. 4, pp. 109-118, 1898. 27‘*The Stratigraphy of the California Coast Ranges,’’ Journ. Geol., vol. 3, no. 4, p. 415, 1903. 28 ‘* Miocene Diabase of the Santa Cruz Mountains in San Mateo County, Cali- fornia,’’ Proc. Am. Phil. Soc., vol 43, pp. 15-53, 1904. 29 Proe. Calif. Acad. Sci., 3d series Geol., vol. 2, no. 2, pp. 156-246, 1905. Proe. Calif. Acad. Sci., 4th series Geol., vol. 3, pp. 1-40, 1908. 430 University of California Publications in Geology [ Vou. 8 he divided the Upper Neocene on the east side of the Coast Ranges in the vicinity of Coalinga, in ascending order, into the Coalinga beds, and the Etchegoin formation, correlating the former with the Upper Miocene and the latter with the Pliocene. Later work in this field has shown that in the region to the northwest of Coalinga, a part of the area mapped by Anderson as Coalinga beds in reality belongs to his Temblor formation, Lower Neocene. To the west and southwest of Coalinga the beds mapped as Coalinga are in part equivalent to the beds mapped by Arnold and Anderson as Jacalitos, a formation to which reference will be made later. Anderson believed the Coalinga beds to be equivalent to the Santa Margarita of Fairbanks, but doubted their equivalence to the San Pablo. On pages 39 and 40 of the second paper cited above, he says: In the former paper the San Pablo, as known from its type localities, was correlated with the Etchegoin; and this seems to be its closest ally among the stratigraphic series farther south, while in the Salinas Valley and elsewhere, beds that have been generally called San Pablo and otherwise correlated with it, are undoubtedly more closely related to the Coalinga. The type locality of Ostrea titan, Tamiosoma gregarea, Pecten estrellanus, P. crassicardo and many other species described by Conrad, was the Estrella Creek where Coalinga beds are abundantly fossiliferous. It yet remains to be shown that these beds are properly correlated with the San Pablo of the type localities; whereas, the fauna of the Coalinga beds are unmistakable in them, as in the Santa Mar- garita beds.’’ In 1906, Arnold®° published a paper on ‘‘The Tertiary and Quar- ternary Pectens of California,’’ in which he gives a brief review of the stratigraphy and palaeontology of the Tertiary formations of Cali- fornia. He recognizes the probable equivalency of the San Pablo to the Santa Margarita of Fairbanks, but is undecided as to the relation of the San Pablo to the Purisima. On page 25 he states: Much uncertainty exists in the mind of the writer as to the exact relation existing between the Purisima and San Pablo formations. After a careful examination of a large amount of material from the type locality of the two formations, and also from the supposedly equivalent formation in the Salinas Valley and adjacent regions, supplemented by field studies at most of the localities from which the material was obtained, it appears evident that the two formations are quite intimately related. It is a complex problem and is one which will require careful field and laboratory study for its solution. The Purisima fauna, taken as a whole, appears to be younger than the aggregate San Pablo fauna and for the sake of convenience wilt be considered as the later of the two. 30U, 8. G. 8. Prof. Paper 47, 1906. 1915] Clark: Fauna of the San Pablo Group 431 One of the first papers published by the United States Geological Survey dealing with the distribution of the oil of California was by George Homans Eldridge,** on the ‘‘Santa Clara Valley Oil District, Southern California.’’ This appeared in 1907 and marks the beginning of a series of publications on the different oil fields of California, which have greatly stimulated the study of the Tertiary palaeontology of California. This paper was edited by Dr. Ralph Arnold after the death of Mr. Eldridge in 1905. The section described is in the vicinity of Santa Clara Valley, Ventura and Los Angeles counties. A very thick series of Upper Neocene, designated the Fernando, is described as overlying the Lower Neocene (the Vaqueros and the Modelo). In speaking of this series Eldridge says: The rocks that have received the name Fernando consist of an enormous succession of conglomerates, sandstones and arenaceous clays, largely of Plio- cene age, developed over considerable portions of Southern California. Fossils collected at many localities and horizons throughout the formation indicate that it extends from the Upper Miocene (San Pablo formation of the general geologic column of the state) well up into the Pleistocene (San Pedro forma- tion). It is possible to subdivide the formation locally on both lithologie and palaeontologie grounds, but taken over a considerable extent of territory these divisions merge into one another both stratigraphically and geographically by insensible gradations. A fairly large fauna is listed from the Fernando on pages 24-28 of this bulletin. The fauna is divided into three separate lists, repre- senting the lower, middle and upper horizons. The author states that —the oldest fauna was found in the area north and northeast of Camulos, and is according to J. C. Merriam, the equivalent of the fauna of at least a part of the San Pablo formation. The middle fauna was found well developed in the region of Elsmere Canon and Fernando Pass and probably represents the typical fossiliferous por- tion of the Purisima and the lower part of the San Diego formation. The upper part of the Fernando extends well up into the Pleistocene, as is attested by the fossils found at Barlows’ ranch and on the south slopes of Mount San Cayetano. The fauna listed from the lower Fernando is now known to belong to a higher horizon than the San Pablo, being as young as or younger than the Etchegoin or Purisima. Further reference will be made to this in the discussion of another paper. The list given on page 26 credited to J. G. Cooper obviously contains the names of a number of incorrectly identified species. For 31U. 8. G. S. Bull. No. 309, pp. 71-101, 1907. 432 University of Califorma Publications in Geology [ Vou. 8 example, Astrodapsis whitneyi, a San Pablo species, and Chione whit- neyi and (Chione) mathewsoni, Oligocene and possibly Lower Neocene species, are reported to be associated with Echinarachnius excentricus, a Recent Echinoid. Dr. C. E. Weaver,*? at the time of the publication of his paper on the Stratigraphy and Palaeontology of the San Pablo, appears to have shared with Arnold the idea of the possible close relationship between the San Pablo and the Purisima. After reviewing Arnold’s and Haehl’s work on the Purisima, he concludes by saying that ‘‘at the present time it is impossible to say whether the two formations are equivalent or not.”’ In 1909 Arnold and Robert Anderson** in a paper on the ‘‘ Geology and Oil Resources of the Santa Maria Oil District, Santa Barbara County, California,’’ gave a correlation table in which the San Pablo is represented as occupying a lower stratigraphic position than the Purisima. In this paper it is stated that certain beds in the Santa Maria Oil Distriet which had been included in the Fernando were to be correlated with Fairbanks’ Santa Margarita and Pismo formations. No species characteristic of the Santa Margarita, however, were listed by them. ~ In 1909 Arnold’s** paper on the ‘‘Palaeontology of the Coalinga District’? appeared. This was followed in 1910 by a final report on the ‘‘Geology and Oil Resources of Coalinga District’’ by Arnold and Robert Anderson. In these papers the marine Neocene, stratigraphie- ally above what is known as the Vaqueros (Lower Miocene), is called Santa Margarita and is correlated with the type section of the Santa Margarita of Salinas Valley. A new formation, the Jacalitos, is de- scribed and the Etchegoin formation, described by F. M. Anderson, is recognized. Arnold recognized the distinctness of the fauna of the Santa Mar- garita as compared with that of the Jacalitos and of the Etchegoin, placing the former in the Middle Miocene and the latter two in the Upper Miocene; he considered the San Pablo of middle California to be equivalent to the upper Jacalitos and lower Etchegoin, and younger than the Santa Margarita. He states: For a number of years the Santa Margarita formation was believed to be the equivalent of the San Pablo formation of the Mount Diablo region, but the stratigraphie work in the Coalinga district has shown it to be older. It is 82 Univ. Calif. Publ. Bull. Dept. Geol., vol. 5, no. 16, pp. 248-269, 1909. 33 U.S. G. S. Bull. 322, 1909. 34U. 8. G. S. Bull. 396, 1909; ibid., 398, 1910. 1915] Clark: Fauna of the San Pablo Group 433 quite evident that the Etchegoin formation represents at least a considerable part of the San Pablo, and as the Etchegoin lies well above the beds contain- ing the Santa Margarita fossils it seems likely that the Santa Margarita formation is in part of greater age than the San Pablo. (Bull. 396, p. 22). The new formation, described by Arnold®* as the Jacalitos, out- crops southwest of Coalinga in the vicinity of Jacalitos Creek, and includes, in part at least, beds mapped as Coalinga by F. M. Ander- son, to which reference has already been made. The Jacalitos, as described, consists of a series of soft, indurated sandstones, gravels and clays, about 3500 feet thick, resting upon a silicious shale lithologically similar to the typical Monterey shale found throughout the Coast Ranges. This shale was questionably referred to the Santa Margarita by Arnold because, at one locality, he states that he found in sand- stones below the shale, fossils which he referred to Tamiosoma gre- garea and Trophon carisaensis and which he believed to be character- istic of the Santa Margarita. The fauna from the upper part of Arnold’s Jacalitos is very similar to that of the Etchegoin and probably belongs to that series. But in the lower part of the formation is a fauna which, as a whole, is some- what different from that of the Etchegoin. Many geologists who have worked in the Coalinga field believe that the shale mapped by Arnold as Santa Margarita ? is in reality Monte- rey shale. The writer will not enter into this controversy, except to state that it is still an open question. It is also thought by certain palaeontologists that Arnold’s belief that the Jacalitos fauna is dis- tinet from that of the Santa Margarita was a mistaken one, and that this fauna is merely a provincial phase of the Santa Margarita, here- tofore unknown. Professor J. P. Smith®* evidently shared this belief when, in his paper on the ‘‘Geologie Range of Miocene Invertebrate Fossils,’’ he divided the fauna of the upper Miocene into a lower Santa Margarita—San Pablo zone, and an upper Etchegoin zone, choosing not to recognize the Jacalitos. The writer will discuss the probable position of the Jacalitos fauna later. In 1911 J. P. Smith*’ published a paper containing a correlation table of the Neocene sections of California. He represented the Kirker Pass section of the San Pablo as equivalent to the Santa Margarita of Salinas Valley, and the San Pablo Bay section as equivalent to the 35 Proe. Calif. Acad. Sci., 2d series Geol., vol. II, no. 2, p. 174, 1905. 36 Proc. Calif. Acad. Sci., 4th series, vol. III, pp. 161-182. April 5, 1912. 37 «The Geologic Record of California,’’ Journ. Geol., vol. 18, no. 3, pp. 216- 227, 1911. 434 University of California Publications in Geology [ Vou. 8 Etchegoin. In a subsequent paper*® he divided the Upper Miocene into two faunal zones, the lower or San Pablo-Santa Margarita zone, and the upper, or Etchegoin zone. In 1914 Mr. W. A. Eneglish*® published a paper on ‘‘The Fernando Group near Newhall, California,’’? in which a list of 79 marine inver- tebrate species is given; these were obtained from the beds at the base of the Fernando, which had been regarded as equivalent to the San Pablo of middle California. The fauna listed by English is obviously much younger than that of the San Pablo and belongs rather to the Pliocene than to the Miocene. English’s conclusions are as follows: “The fauna listed by Arnold and Anderson from the Etchegoin of Coalinga contains eighty-four determined species, of which eighteen are common to the lower Fernando, ten of these being found in the Purisima also. Most of the species common to the Fernando and the Etchegoin have an extended vertical range, so that the relationship is not so definitely shown as between the Fernando and the Purisima. It is probable that the lower Fernando and the Etchegoin do not differ greatly in age.’’ PosITION OF SAN PABLO IN THE NEOCENE SECTION OF CALIFORNIA Relation to Etchegoin and other Formations correlated with the San Pablo—The fauna of the San Pablo is distinctly older than that of the Etchegoin and certain other local California formations with which the latter has been correlated, including the Purisima, Merced, Fernando, Wildcat and the Pliocene deposits at San Diego and San Pedro. A comparison of the fauna of the Etchegoin, as listed by Arnold (Bull. 306, U.S. G. S., pp. 30-36), with that of the San Pablo shows some striking differences. The number of species common to the two is 38, or 25+ per cent, of the determinable species in the San Pablo; of these nearly all are either Recent or have a long range and are not generally recognized as good horizon determiners. For example, none of the Pecten species and none of the echinoderms of the San Pablo are found in the Etchegoin or in the other formations with which the latter is correlated. Again, the Etchegoin contains a larger percentage of Recent species. Arnold states the percentage of Recent forms in the Etchegoin to be 35. Later collecting in the Etehe- goin has increased this percentage to over 40. The percentage of 38 “Geologie Range of Miocene Invertebrate Fossils of California,’’ Calif. Aead. Sei., 4th series, vol. III, p. 161, 1912. 39 Univ. Calif. Publ. Bull. Dept. Geol., vol. 8, no. 8, pp. 203-218, 1914. 1915] Clark: Fauna of the San Pablo Group 435 Recent mollusean species to the total determinable number of mollusean species in the San Pablo is 23+, or about half that of the Etchegoin. A comparison of the percentage of Recent gastropods in the fauna of the Etchegoin with the percentage of Recent gastropods in the San Pablo also shows a striking difference. In the Etchegoin 25 per cent of the gastropods listed by Arnold are Recent. In the San Pablo the percentage of Recent is 11. Only eleven species of the gastropods found in the San Pablo of Middle California are found in the Etchegoin. Relation to Santa Margarita—A survey of the fauna from the Santa Margarita of the type area and of the area north of Coalinga shows that it is much more closely related to the fauna of the San Pablo than to that of the Etchegoin. About one-half of the known species of the Santa Margarita are also found in the San Pablo of Middle California. The species which are common to the San Pablo and the Santa Margarita of the south are forms which are generally recognized as being good horizon determiners, such as the echinoderms, and the more highly ornamented peleeypods and gas- tropods. The Santa Margarita north of Coalinga apparently represents only the Astrodapsis whitneyi zone of the San Pablo group of middle California. In the vicinity of Oilfields, the fossiliferous marine beds of the Santa Margarita are a little over 400 feet thick, and Astro- dapsis whitneyi occurs throughout the section. Here it is associated with species common to the Astrodapsis whitneyi zone of the San Pablo of Middle California, such as Venus martini, Dosinia merriami, var. occidentalis, Dosinia arnoldi, Ostrea titan, Pinna alamedensis, Can- cellaria pabloensis, and Trophon carisaensis. None of these have been found in either the Lower San Pablo, or in the Etchegoin. The fauna from the Santa Margarita on the west side of the Coast Ranges is as yet imperfectly known. The Astrodapsis whitneyi zone is present and probably beds equivalent to the lower San Pablo of Middle California are also represented. Relation to Jacalitos—The fauna above the Astrodapsis whitneyi zone of the San Pablo of Middle California is not represented in the Santa Margarita section north of Coalinga. This upper fauna may possibly be in part equivalent to that of the Jacalitos of Arnold. This probable relationship is suggested by the presence in the Jacalitos of such species as Astrodapsis, ef. tumidus, large variety, Cyrena (Cor- bicula) californica, Mulinia, ef. pabloensis, Pecten, aff. crassicardo, 436 University of California Publications in Geology [ VoL. 8 Pecten estrellanus and Zirphaea, ef. dentata, all of which are found in the San Pablo but do not extend into the Etchegoin. On the other hand, the presence of many species in the Jacalitos which range into the Etchegoin but which have not been found in the Santa Margarita of the south or in the San Pablo of Middle California would seem to suggest a later age than the upper San Pablo of Middle California and therefore a considerably later age than the Santa Margarita north of Coalinga. Some of the Etchegoin-Jacalitos forms which have not been found in the San Pablo or Santa Margarita are Hchinarach- nius gibbsi, Cardium, ef. meekianum, Macoma vanlecki, Mya japonica, Pecten owen, Chrysodomus portalensis, Thais lamellosa, Thais etche- goinensis, Thais kettelmanensis and Turritella vanvleckt. It is the writer’s opinion that the Jacalitos beds are probably younger than the uppermost beds of the San Pablo of middle California and that future work will show that they have a closer relationship to the Etchegoin than to the San Pablo. Relation to the Scutella breweriana beds.—It has been shown in the descriptions of the different sections that in some localities it is difficult to draw a sharp line between the Monterey and the San Pablo groups. As has already been stated, the writer, in his description of the San Pablo of middle California, originally accepted the line be- tween it and the underlying Monterey group as first defined by Pro- fessor J. C. Merriam, which line of division has been accepted by Professor A. C. Lawson in mapping beds of these horizons in this part of the state. (See folio U. S. G. S. No. 193.) At the present time, however, the writer is of the opinion that the Seutella breweriana beds, which have been considered as a part of the Monterey group by Merriam and Lawson, should be classed as either a part of the San Pablo group or as a distinct stratigraphic unit. On the north side of Mount Diablo there is a good unconformity between the San Pablo and the Monterey group, but in this region the Scutella breweriana beds are not present. Reference has already been made to an irregular contact on the south side of Mount Diablo which was regarded as the dividing line between the San Pablo and the Seutella breweriana beds. However, this contact is of such a character that it might be merely a local unconformity. In all the other sections studied by the writer no stratigraphic break between the Seutella breweriana beds and the San Pablo was apparent, and at some localities the division was made purely on the basis of the faunas; at other places, however, especially 1915] Clark: Fauna of the San Pablo Group 437 in the San Pablo Bay section, and eastward as far as the town of Walnut Creek, the change in fauna was accompanied by a change in lithology. The physical evidence seems therefore to show that, with local exceptions, the San Pablo conformably overlies the Scutella breweriana zone. This is apparently corroborated by the close faunal relationship existing between the two, which was first pointed out by Professor Merriam.*® Weaver*! recognized this fact when he said: ““The Upper Monterey faunal zone is very closely allied to the San Pablo, and where the two lie in contact it becomes very difficult to draw the line of separation.’’ Out of a known fauna of about sixty species from the Seutella breweriana zone, about 50 per cent are also found in the San Pablo. A number of species, however, appear to be char- acteristic of this zone and have not been found in the San Pablo. More collecting may show that the fauna from the Scutella breweriana zone is more distinct than it now appears. There is a much greater differ- ence between the faunas of the Seutella breweriana zone, and of the Lower Monterey (Agasoma gravadum zone) as known at. present, than exists between the fauna of the Scutella breweriana zone and that of the Lower San Pablo. Stratigraphic as well as faunal evidence seems to bear out the con- clusion that Seutella breweriana beds should be separated from the Monterey. The writer will reserve the discussion of the details of this evidence for a later paper. AGE OF THE SAN PaBLo Two of the most important methods which at least theoretically may be applied in the determination of the age of the San Pablo, with reference to the different horizons of the east coast and of Europe, are the ‘“‘percentage method’’ and the identity of species. In applying the ‘‘percentage method’’ we have a means of correlation the principle of which is generally accepted, but as to the practical application there is considerable disagreement. One of the first to use the percentage method in order to determine relation of the age of the Neocene horizons of the West Coast was W. H. Gabb.*® As has already been pointed out, he placed beds that are referred to in this paper as the San Pablo Group in the Pliocene. 40 Merriam, J. C., Univ. Calif. Publ. Bull., Dept. Geol., vol. 3, no. 16, p. 378, 1904. 41 Univ. Calif. Publ. Bull. Dept. Geol., vol. 5, no. 16, p. 267, 1909. 42 Gabb, W. H., Palaeontology of California, vol. 1, p. 31. 438 University of California Publications in Geology [Vou. 8 This was determined on the basis of the great number of Recent species in the fauna obtained from those beds. Using the same method he placed beds which, in part, correspond to the Monterey Group, in the Miocene. C. E. Weaver,** in his paper entitled ‘‘Stratigraphy and Palaeon- tology of the San Pablo Formation in Middle California,’’ placed the San Pablo in the Pliocene, because of the great number of Recent species which the fauna contained. Using in part this same method, Dr. Ralph Arnold in his paper on the Palaeontology of the Coalinga District, determined the Etchegoin, which is now known to be younger than the San Pablo, to be of Mio- cene Age. The following is quoted from page 46 of Arnold’s* paper: According to the list given in this paper, the Etchegoin is represented by 84 recognizable species; of these, 55 species or varieties (65%) are extinct, while 27 species (35%) are still living in the Pacific Ocean. According to Lyell’s classification this would place the formation decidedly in the Miocene. It is now generally recognized by palaeontologists that the per- centages used by Lyell in applying the ‘‘ percentage method’’ must be modified to meet the modern refinement of species. Such a modifica- tion has already been attempted in the Neocene of Europe and in the Neocene of the east coast of North America. W. Hi. Dall,’ in his paper ‘‘The Relation of the Miocene of Europe to that of other Regions and to the Recent Fauna,’’ states that in the molluscan fauna of the Maryland Miocene only 10 per cent of the species survive. He says: This small number is partly the result of the rather restricted limits adopted for species by the authors of this part of the volume as compared with the views prevalent in the time of Lyell. However, about 13% of the New Jersey species survive and 14% of the Floridan Chesapeake, so the esti- mate is not far from the normal for the Lower American Miocene. For the Upper Miocene of Duplin about 20% are estimated to survive and 19% in the Suffolk district of Virginia. The intermediate Yorktown beds have about 17% of survivors. In this paper Dall shows that the percentages of Recent species from the different horizons of the east coast Miocene agree fairly well with those of the corresponding horizons of the European Miocene and apparently the correlation of these different horizons of the Miocene 43 Univ. Calif. Publ. Bull., Dept. Geol., vol. 5, no. 16, pp. 268-269. 44 Bull. U. 8. G. S., no. 396, 1909. 40 W. H. Dall, Maryland Geol. Survey. Miocene Text, pp. 49-50, 1904. — —— 1915] Clark: Fauna of the San Pablo Group 439 and Pliocene of Europe and the east coast of North America has been, at least approximately, established on the basis of the percentage method. The percentage of Recent molluscan species in the San Pablo of Middle California as listed by the writer is 23+; as based upon the gastropods the percentage is only 11 per cent. If we use the per- centages as applied to the east coast Neocene and if we can rely upon the equal refinement in the determination of the species, the San Pablo may be considered to be Upper Miocene in age, possibly Lower Pliocene. Accepting this determination of the age of the San Pablo, the Etchegoin and other formations which are equivalent to it must of necessity be Pliocene in age. This determination is borne out by the high percentage of Recent species in the latter horizon. As yet no satisfactory correlation has been made between the west coast and the east coast of North America or with Europe on the basis of identity of invertebrate species. The marine molluscan fauna of the east coast of North America, except for a few cireumboreal species, is almost entirely different from that of the west coast. In general it may be said that for every coast of the different continents there is a distinct molluscan faunal province and on each coast there are distinct subfaunal provinces. The great differentiation in molluscan faunas which we find at the present day apparently also existed during the Neocene. Very few species, if any, of the marine molluscan faunas of the Neocene of the west coast are found in the Neocene of the east coast or of Europe. The difficulty in correlating the Neocene of different parts of the west coast, as between Washington and California, also shows that local faunal provinces existed then as at the present time. The same factors which have brought about the differentiation of the mollusean faunas of the Neocene and Recent over a large part of the world have produced the generalization of the land vertebrate faunas. The close connection of the great continental masses during the Neocene, separating seas which had previously been united, to- gether with the well-marked climatic zones, isolated the invertebrate faunas of the different coasts and therefore brought about their differentiation. This allowed a wide migration of the vertebrate forms, the faunal provinces being enlarged so as to inelude more than one continent. From the above facts it would seem self-evident that if determin- able land vertebrates could be found in the west coast marine Neocene 440 University of California Publications in Geology [ Vou. 8 section, a correlation might be made with Europe which would be more accurate than anything that has as yet been made. Recently some important discoveries of land vertebrates were made in the region of Oilfields, Fresno County, California, by a party sent out by the University of California. It is believed that these dis- coveries have a very significant bearing on the correlation of the Neocene of the west coast with the European type section of the Miocene and Pliocene. Land vertebrates were found in the section referred to above at four different horizons. The most important collection was obtained from the upper beds of the Temblor (‘‘Lower Neocene,’’ called Vaqueros by Anderson and Arnold, Bulls. Geol. 306 and 308, U. S. G.S.). Here numerous well-preserved teeth of the genus Merychippus, a Miocene three-toed horse, were found with a number of other forms, such as mastodon, pececary, and camel. These land vertebrates were below strata containing a typical Temblor invertebrate fauna, the beds from which the fossils were obtained evidently being estuarine or delta deposits. For the details concerning the fauna of the Merychippus zone, the reader is referred to Professor J. C. Merriam’s*® paper entitled ‘‘Correlation between the Tertiary of the Great Basin and that of the Marginal Marine Province in California.’’ A full dis- cussion is given in this paper concerning the importance of this fauna as a means of determining the age of the Temblor beds. Professor Merriam’s final conclusion is that ‘‘the fauna of the Merychippus zone is near the stage of the Middle Miocene as represented by the Maseall and Virgin Valley faunas of the Great Basin region and by the Paw- nee Creek stage of the Great Plains area.’’ In the north Coalinga section, to which reference has just been made, the Temblor beds are overlain unconformally by beds known as the Santa Margarita formation, which corresponds in part to the San Pablo Group of Middle California. The Santa Margarita of the Coalinga District does not include as much as the San Pablo Group of Middle California. The Lower San Pablo and the Seutella brewer- lana zone are apparently missing in the north Coalinga section. The writer has already expressed the opinion that the Seutella breweriana beds are younger than the typical Monterey, to which the Temblor belongs, and that the stratigraphic evidence shows that there is a con- siderable time break between the two stratigraphic zones. There is 46 Science, n. s., vol. XV, no. 1035, pp. 648-645, August, 1914; also paper in press, Trans. Amer. Phil. Soc. 1915] Clark: Fauna of the San Pablo Group 441 good faunal evidence to show that both the Lower San Pablo and Seutella breweriana zone belong to a later horizon than the Temblor and Merychippus zone. During the time represented by the uncon- formity between the Temblor and Santa Margarita of this district, beds belonging to the Seutella breweriana zone and the Lower San Pablo were being deposited. It will be very readily seen that the determination of the Upper Temblor as Middle Miocene has a very important bearing on the age of the San Pablo and of the Scutella breweriana zone. The lower limit of the latter can probably not be below upper Middle Miocene. The San Pablo being younger than the Seutella breweriana zone may pos- sibly have its lower limit near the lower part of the Upper Miocene. However, it must be admitted that this determination of the lower limit of the San Pablo is rather indefinite, first, because we are not certain of the relation of the Scutella breweriana beds to those of the Lower San Pablo; second, because at present it is impossible to esti- mate the length of time represented by the hiatus between the beds of the Temblor and the Scutella breweriana zone. The best evidence that we now have as to the age of the uppermost beds of the San Pablo is also derived from land vertebrate fossils. The writer has already shown that the fauna of the Etchegoin is distinetly younger than that of the San Pablo. In the region of Oilfields, Fresno County, California, immediately to the north of Coalinga, the Santa Margarita, which here is equivalent to that of the Upper San Pablo of Middle California known as the Astrodapsis whitneyi zone, is over- lain unconformably by about 1800 feet of beds which have been re- ferred questionably by Arnold and Anderson* to the Jacalitos Forma- tion. No invertebrate species have been obtained from these beds and there is a question as to their exact correlation with the known marine horizons. This fact is to be noted, however, that these 1800 feet of strata lie unconformably above the Santa Margarita and are below the type section of the Etchegoin, the latter of which was considered by Arnold to be Miocene in age. In the lower beds of the Jacalitos? ver- tebrate remains were found by the University of California party referred to above. Professor Merriam from this vertebrate evidence believes that the Lower Jacalitos? is near the age of the Rattlesnake or Thousand Creek beds which are referred to the early Pliocene. The problem is complicated at this point by the fact that we do not have marine invertebrates associated with the vertebrates found 47 Bull. U. S. G. S., 398, p. 107, 1910. 442 University of California Publications in Geology [ Vou. 8 in the Lower Jacalitos(?). If these beds, which appear to be land or estuarine in origin, prove to be of the same age as those of the typical Jacalitos on Jacalitos Creek to the southwest of Coalinga, then possibly we may be able to determine the upper limit of the San Pablo quite accurately. Another horizon from which land vertebrates were obtained was in the type section of the Etchegoin. Horse teeth of the genus Proto- hippus, together with a number of other forms, were secured in the basal beds of the Etchegoin. This fauna together with the vertebrate evidence of the basal beds of Jacalitos?, stratigraphically 1800 feet lower, shows quite conclusively that the Etchegoin is distinctly Plio- cene rather than Miocene. Probably the best evidence showing the age of the uppermost beds of the San Pablo of Middle California comes from vertebrate material obtained in the fresh-water beds which in Middle California overlie unconformably the San Pablo Group. This material was described by Professor J. C. Merriam*® in his paper ‘‘Vertebrate Fauna of the Orindan and the Siestan Beds in Middle California.’’ His conclusions as to the age of these beds as shown by the vertebrates was as follows: The mammalian remains known from both the Orindan and Siestan up to the present time all represent forms such as might be expected in the late Miocene or in the earliest Pliocene, but it will be necessary both to have better material from the Orindan and Siestan and to have well-known faunas of western Miocene and Pliocene for comparison before the last word on the age determination can be pronounced. Considering the indefiniteness of all the factors concerned, one would not seem justified in being more definite than to state that the Orindan and Siestan faunas are near a late Miocene stage. When the faunas of the two formations are better known, it may appear that more than one stage is represented. CONCLUSIONS (1) The San Pablo division should be designated a group rather than a formation, as these terms are used by the United States Geo- logical Survey. (2) The Neocene of California is divisible into at least three dis- tinct stratigraphic groups, which in this paper are called Lower, Mid- dle, and Upper Neocene; the San Pablo group represents the Middle Neocene; the Lower Neocene is represented by the Monterey group, including the Vaqueros, Temblor, and Monterey shale; the Upper 48 Univ. Calif. Publ. Bull., Dept. Geol., vol. 7, no. 19, pp. 384-885, 19138. 1915] Clark: Fauna of the San Pablo Group 443 Neocene by the Etchegoin, Merced, Purisima, Wildeat, and Fernando eroups, and by the San Pedro and San Diego Pliocene. (3) The fauna of the San Pablo group of Middle California is divisible into two major zones. These are quite distinct as shown by the mollusks and the echinoderms. Each of the zones is again divisible into minor faunal zones which are based largely upon the restricted range of echinoderm species, but in part upon the similarly restricted range of some of the mollusks. (4) The San Pablo deposits are for the most part of true marine origin. In certain sections, however, beds are found at different levels, which appear to have been deposited under estuarine, brackish-water, or questionably fresh-water or land conditions; these appear to repre- sent local uplifts about the border of the basin of deposition. (5) The temperature of the San Pablo sea was about the same as that of the waters now found along the coast of Middle California be- tween Point Conception and Santa Barbara. (6) A large percentage of the extinct species in the San Pablo are closely allied to species living on the California coast at the present time, the latter forms being descended from the earlier species. (7) The age of the San Pablo group is believed to be Upper Mio- cene; this is determined first, by the low percentage of Recent species in the group; and, second, by evidence afforded by the vertebrate material found above and below the group. (8) The San Pablo beds of Middle California are correlated with the Santa Margarita formation in San Luis Obispo County as de- scribed by Fairbanks, and with the beds mapped as Santa Margarita in the Coalinga oil field and in the southwest end of the San Joaquin Valley. (9) The San Pablo group is distinctly older than the Etchegoin, Purisima, Merced, Fernando, and Wildcat formations, and older than the San Pedro and San Diego Plocene. 444 University of California Publications in Geology [ Vou. 8 BIBLIOGRAPHY ANDERSON, F. M. A Stratigraphie Study in the Mount Diablo Range of California. Proce. Calif. Acad. Sci., 3d series, Geol., vol. 2, no. 2, pp. 156-246, 1905. A Further Stratigraphic Study in the Mount Diablo Range of California. Proe. Calif. Acad. Sci., 4th series, Geol., vol. 3, pp. 1-4, 1908. ARNOLD, RALPH. Tertiary and Quaternary Pectens of California. U. 8S. G. 8. Prof. Paper, 47, 1906. Palaeontology of the Coalinga District. U.S. G. 8. Bull., 396, 1909. ARNOLD, RALPH, and ANDERSON, Rost. Geology and Oil Resources of the Santa Maria Oil District, Santa Barbara County, California. U.S. G. 8. Bull., 322, 1909. Geology and Oil Resources of the Coalinga District. U.S. G. 8. Bull. 398, 1910. ARNOLD, RALPH, BRANNER, J. C., and Newsom, J. J. Santa Cruz Folio, No. 163, 170. ASHLEY, G. H. The Neocene Stratigraphy of the Santa Cruz Mountains in California. Proe. Calif. Acad. Sci., 2nd series, vol. 5, pp. 273-367, 1895. CLARK, B. L. The Neocene Section at Kirker Pass on the North Side of Mount Diablo. Univ. Calif. Publ. Bull. Dept. Geol., vol. 7, no. 1, pp. 47-60, 1912. ConrRaD, T. A. Report on the Palaeontology of the Survey. Pac. R. R. Reports, vol. 7, pp. 189-196, pls. 1-10, 1859; Appendix to report of Thomas Antisell. Descriptions of New Marine Shells from Upper California Collected by Thomas Nuttall. Journ. Acad. Nat. Sei., Philadelphia, vol. 7, pp. 227- 268, pls. 17-20, 1834. Description of three new Genera, twenty-three new Species of Middle Ter- tiary Fossils from California, and one from Texas. Proce. Acad. Nat. Sci. Phil., vol. 8, pp. 312-316, 1857. Description of Tertiary Fossils Collected on the Survey. Pac. R. R. Reports, vol. 6, part A, no. 2, pp. 66-73, pls. 2-5, 1857; Appendix to report of Dr. J. S. Newberry. Cooprr, J. G. Catalogue of California Fossils. 7th Ann. Rept. Calif. State Min. Bur., pp. 221-308, 1880. Datu, W. H. The Relation of the Miocene of Europe to that of other Regions and to the Recent Fauna. Maryland Geol. Sury. Miocene, Text, 1904. Miocene of Astoria and Coos Bay, U. 8. G. 8. Prof. Paper, 59, pl. 14, figs. 1-11, 1909. Wagner Free Institute of Science., vol. 3, pt. 3, 45 and 46, 1895-1903. ELDRIDGE, GEORGE HoMANS. Santa Clara Valley Oil District, Southern California. U. 8. G. S. Bull. 309, 1907. ENGLISH, W. A. The Fernando Group near Newhall, California. Univ. Calif. Publ. Bull., Dept. Geol., vol. 8, no. 8, pp. 208-218, 1914. 1915] Clark: Fauna of the San Pablo Group 445 FAIRBANKS, W. H. The Stratigraphy of the California Coast Ranges. Journ. Geol., vol. 3, no. 4, p. 415, 1903. San Luis Folio No. 101, U. S. G. S. Publ., 1904. Gass, W. M. Geological Survey of California, Palaeontology, vol. 2, pp. 1-299, pls. 1-36, 1869. HAEHL, H. L., and ARNOLD, RALPH. Miocene Diabase of the Santa Cruz Mountains in San Mateo County, Cali- fornia. Proce. Amer. Phil. Soc., vol. 48, pp. 15-53, 1904. JONES, W. F. 4 Geology of the Sargent Oil Field. Univ. Calif. Publ. Bull., Dept. Geol., vol. 6, no. 3, pp. 55-78, 1911. Lawson, A. C., and PALACHE, C. The Berkeley Hills, a Detail of Coast Range Geology. Univ. Calif. Publ. Bull. Dept. Geol., vol. 2, no. 12, pp. 349-450, 1902. MerRiAM, J. C. The Distribution of the Neocene Sea-Urehins of Middle California. Univ. Calif. Publ. Bull. Dept. Geol., vol. 2, no. 4, pp. 109-118, 1898. The Tertiary Sea-Urchins of Middle California. Proce. Calif. Acad. Sci., 3d series Geol., vol. 1, pp. 161-175, 1899. NEWBERRY, J. S. Pac. R. R. Rept., vol. 6, pp. 13-14. REMoND, AUGUST. Description of Two New Species of Bivalve Shells from the Tertiaries of Contra Costa County. Proe. Calif. Acad. Nat. Sei., vol. 3, pp. 13-14, March, 18638. Description of Four New Species of Echinodermata from the Tertiaries of Contra Costa County. Proce. Calif. Acad. Sci., vol. 3, pp. 52-54, August, 1863. SHUMARD, B. F. Descriptions of New Fossils from the Tertiary formation of Oregon and Washington territories and the Cretaceous of Vancouver Island. Col- lected by Wr. John Evans, U. S. Geologist, under instructions from the Department of the Interior. Transactions U. 8. G. S. No. 59, p. 126, 1858. SmirH, J. P. The Geologic Record of California. Journ. Geol., vol. 18, no. 3, pp. 216- 227, 1911. Geologic Range of Miocene Invertebrate Fossils of California. Proe. Calif. Acad. Sci., 4th series Geol., vol. 3, pp. 161-182, 1912. TuRNER, H. W. Geology of Mount Diablo, California. Bull. Geol. Soe. Amer., vol. 2, pp. 383, 414, 1891. ' The Rocks of the Mount Diablo Range of California. Journ. Geol., vol. 6, pp. 498-499, 1898. Weaver, C. E. Stratigraphy and Palaeontology of the San Pablo Formation in Middle Cali- fornia. Univ. Calif. Publ. Bull. Dept. Geol., vol. 5, no. 16, pp. 243-269, 1909. A Preliminary Report on the Tertiary Palaeontology of Western Washington. Wash. Geol. Surv. Bull., no. 15, pp. 1-80, pls. 1-15, 1912. WHITNEY, J. D. Geological Survey of California, vol. 1, p. 31, 1865. 446 University of California Publications in Geology [ Vou. 8 DESCRIPTION OF SPECIES PELECYPODA YOLDIA CARNAROSENSIS, n. sp. Plate 48, figure 6 Shell medium in size, beaks low and inconspicuous, situated about two-thirds the distance from the anterior to the posterior end. An- terior dorsal edge long and very gently convex; posterior dorsal edge gently concave. Posterior extremity subtruncate to bluntly rounded, the blunt subtruncate end being subangulate at the junction with the posterior dorsal edge and indistinctly separated from the ventral edge. Surface sculptured by somewhat irregular incremental lines or con- centric ribs. On the surface near the posterior end there is a distinct suleus which reaches from the beak to a little below the angulation on the posterior end. Hinge plate unknown. Y. carnarosensis, n.sp., somewhat resembles Y. cooperi Gabb, a recent West Coast species. It differs in the following respects: the posterior end is not so attenuated, the concentric ribbing is not so regular, the distinct suleus on the posterior extremity is lacking on Y. coopert. Dimensions.—Lenegth about 40 mm.; height 20 mm. Occurrence—F rom San Pablo Group, Carnaros Creek, Napa County. PINNA ALAMEDENSIS Yates Plate 48, figure 3 Pinna alamedensis Yates. Rept. State Mineral. cf Calif., 1887, p. 259. Pinna alamedensis Yates. Calif. State Mining Bureau, Bull, no. 4, 1894, p- 56, pl. IV, fig. 53. This species has nine concentric inequidistant rounded wrinkles emanating from the open side, and turning toward the hinge at nearly right angles, the entire shell marked by longitudinal narrow ribs (about forty), which, radiating from apex, extend to the basal margin, becoming more indistinct as they ap- proach the lower margin. These ribs, at their intersection with the lines of growth, are ornamented by slight elevations, forming zigzag markings along the lines of growth. The hinge side is straight the entire length, the opposite side running parallel for about one-half the distance from base to apex, where it makes a sharp curve, thence at an angle of about forty-five degrees to the apex. Length 9, width 5, and thickness about 2 inches. Loeality, Alameda Creek, Alameda County. Only one specimen found, and that a very fine one, in the center of a round sandstone bowlder. Miocene. 1915] Clark: Fauna of the San Pablo Group 447 P. alamedensis Yates is a very common species in the Upper San Pablo Group, of which it appears to be characteristic. It is notice- able for its large size and the thickness of the prismatic outer layer. Some of the specimens collected have a maximum antero-posterior length of ten inches, with a maximum width at right angles to that of about five and one-half inches. OSTREA BOURGEOISIT Rémond Plate 43 Ostrea bourgeoisti Rémond. Proce. Calif. Acad. Sci., vol. 3, p. 13, 1863. Ostrea bourgeoisii Rémond. Palaeontology of California, vol. 2, p. 36, pl. 11, fig. 57, 57a, 1863. The description is from two lower valves, from the collections of Mr. 1’Abbé Bourgeois (Pont-Levoy, France), and Mr. Pioche (San Francisco). Shell sub-oval, higher than long, strongly contracted near the cardinal area, sub-rounded on the ventral margin; inferior valve comparatively thin, convex, irregular exteriorly, with remote, somewhat rugose, plaits of growth. Liga- ment fosset long, profound, minutely wrinkled and finely striated, oblique and turned downwards; muscular impression very large, oblique, and sub-central somewhat prominent. Locality: vicinity of Kirker’s Pass, from a late Tertiary bed. ? O. bourgeoisti Rémond has been confused in the past with O. titan Conrad. The writer in a previous paper (Univ. Calif. Publ. Bull. Dept. Geol., vol. 7, no. 4, p. 54, 1912) listed it as O. titan Conrad. Other writers previous to this made the same mistake. Gabb reports O. titan Conrad from Kirker Pass. All the specimens that the writer has seen from that locality, including specimens of the old State Survey in the collections of the University of California and labeled O. titan Conrad, belong to the species O. bowrgeoisti Rémond. So far the writer has not seen a specimen of OQ. titan Conrad from the Lower San Pablo group or the upper part of the Monterey group. In the Lower Monterey there is an oyster that is very close to, if not identical with, O. titan Conrad as seen in the Santa Margarita beds of San Luis Obispo County. O. bourgeoisii Rémond somewhat resembles O. titan Conrad in its size and thickness, though it is never as large. The maximum length as measured from the beak through the muscle impression is about eight to ten inches, with a maximum width at right angles to this of about five inches. Both valves vary considerably in thickness; some- times the shell of the ventral valve has a thickness of from two to three inches. The ventral valve is usually only slightly more convex than 448 University of California Publications in Geology [ Vou. 8 the upper valve but is usually somewhat thicker. The fine radiating ridges on the surface, described by Rémond, are not constant, ap- pearing on only a few specimens that the writer has seen. O. bourgeoisii Rémond differs from O. titan Conrad in that the ligamental pit is narrower and the ligamental callus is heavier; on Ostrea titan Conrad the ligamental pit extends nearly across the an- terior end of the shell; the muscle impression on O. bourgeoisii Rémond is much smaller and is nearer the posterior end of the shell than on O. titan Conrad; on the latter species the muscle impression is some- times nearly half the width of the shell; the ventral valve of O. titan Conrad is usually more strongly convex. A large number of specimens of both species were examined and these differences were found to be constant. Occurrence—Very common in the Lower San Pablo group at Kirker Pass, University of California locality 2140; also from the south side of Mount Diablo in the Lower San Pablo Group and Upper Monterey Group. PECTEN (PLAGIOCTENIUM) BILINEATUS, n. sp. Plate 64, figures 3 and 4 Shell thin, medium in size, equivalved and equilateral, usually longer than high. Dorsal edges gently concave, the anterior dorsal edge usually being shorter than the posterior; ventral edge quite strongly and regularly arcuate. Apical angle averaging about 102°. Hinge plate about half as long as the length of the shell. Both valves gently convex and similarly sculptured by 18 to 20 low, flat-topped, radiating ribs with interspaces little wider than the tops of the ribs. In each interspace and almost filling it there is a low, broad, flat- topped interrib. On some specimens these broad interribs become almost as prominent as the ribs themselves; this is more especially noticeable near the dorsal edges, where the ribbing becomes finer. Anterior ear of right valve notched, bearing three to four fine, radi- ating riblets; posterior edge of posterior ear slightly oblique, bearing very faint, almost obsolete, radiating riblets. Ears of left valve similar to those of the right valve, except that the anterior ear is not notched. P. bilineatus, n.sp., has been confused with P. raymondi, n. sp., and P. pabloensis Conrad, which species also occur in the same locality. Arnold’s description of P. pabloensis Conrad (U.S. G. S. Prof. Paper, No. 47, pp. 87-89) in part applies very well to P. bilineatus rather than to what is taken by the writer as being the true P. pabloensis Con- EE o 1915] Clark: Fauna of the San Pablo Group 449 rad. Arnold figured P. pabloensis as three distinct species, which are seen on Plate XXVII of the publication mentioned above. Figure 5 represents a very good specimen of the left valve of P. pabloensis Conrad. Figure 6 represents a good specimen of a right valve of P. bilineatus, n.sp., while Fig. 7 appears to represent a left valve of P. raymondi, n. sp. P. bilineatus, n.sp., differs from P. pabloensis Conrad in that the ribs are wider and not so far apart, they do not show the tendency to split as in the other species, the interrib is much broader. The con- centric sculpturing is different, on P. pabloensis Conrad it is distinctly imbricated, the species belonging to the same subgenus as Pecten has- tatus Sowerby—that is, Chlamys; on P. bilineatus it is not imbricated. P. bilineatus resembles P. raymondi, n. sp., in the number and width of the ribs, in the width of the interspaces, and in general outline; it differs from that species in the following respects: it has a thinner shell, the ribs are not so prominent; on P. raymondi there is no inter- rib; the two valves of the latter are unequal, the right valve being flat and the left valve convex, thus belonging to the subgenus Pecten; the valves of P. bilineatus are both convex, the species belonging to the subgenus Plagiocteniwm. Dimensions. —Of type (pl. 64, fig. 3), a right valve, length 45 mm. ; height 38 mm. Occurrence.—This species occurs in the famous Pecten beds on San Pablo Bay near the town of Rodeo, University of California loeal- ity 1632. PECTEN (PECTEN) CIERBOENSIS, n. sp. Plate 47, figure 6 Shell rather small; apical angle about 90°; dorsal edges slightly concave; ventral edge very strongly arcuate. Surface sculptured by fifteen fairly coarse, flat-topped ribs with flat-bottomed interspaces about as wide as the tops of the ribs, interspaces and ribs narrowing rapidly toward the beak, incremental lines inconspicuous. Anterior ear with four fairly heavy radiating ribs; bysal notch deep; anterior edge broken; posterior ear broken. The writer has only one specimen of the right valve of this species, but it appears to be so distinct as to be worthy of a specific name and description. Dimensions.—Leneth, 22 mm.; height, 24 mm. Occurrence.—In the basal beds of the San Pablo Group of the type section. 450 University of California Publications in Geology [ Vou. 8 PECTEN (PLAGIOCTENIUM ?) CRASSIRADIATUS, n. sp. Plate 47, figure 7 Shell medium in size; fairly heavy; apical angle about 98°; height about equal to the length; dorsal edges nearly straight. Hinge plate over half the length of the shell. Right valve sculptured by sixteen heavy, broadly rounded, radiating ribs, which become somewhat nar- rower near the margins; interspaces very narrow and deep. Dorsal margins rather strongly depressed, the depressed area being narrow and without ribs. Anterior ear longer than posterior, deeply notched with anterior edge gently convex, sculptured by four fairly heavy radiating ribs. Left valve unknown. This species appears to be quite unique. The writer has seen only one specimen of the right valve. Dimensions.—Height 47mm.; length apparently about the same as height. Occurrence.—In the lower San Pablo, associated with Astrodapsis tumidus, subsp. cierboensis, Scutella pabloensis, Chrysodomus pablo- ensis, ete., University of California locality 367. PECTEN (PECTEN) RAYMONDI, nu. sp. Plate 46, figures 1 and 2; plate 47, figures 1 and 2 Shell rather heavy, subcireular, nearly equilateral, inequivalved ; hinge line averaging slightly more than one half the leneth of the shell; height about equal to length. Anterior ears slightly longer than posterior ears. Apical angle about 102°. Dorsal edges slightly con- cave; posterior edge longer than anterior edge. Left valve ventricose, sculptured by seventeen to twenty squarish to slightly rounding, heavy, radiating ribs, the interspaces averaging about the same width as the ribs; on some specimens the ribbing tends to become a little finer toward the dorsal edges than on the middle of the disk. Surface also covered by medium fine to coarse concentric lines of growth. Anterior ear sculptured by three to five medium fine radiating ribs; anterior margin of ear slightly notched. Posterior ear with four to five radiating ribs, posterior edge straight, and sloping forwards. Right valve flat, sculptured by seventeen to twenty radiating flat- topped ribs which are usually not as prominent as the ribs of the left valve. On some of the smaller specimens the right valve is slightly ventricose but never so much as the left valve. Interspaces between 1915] Clark: Fauna of the San Pablo Group 451 radiating ribs about equal in width to that of ribs. Concentric lines of growth usually not so heavy as on left valve. Anterior ear deeply notched, sculptured by three to five medium fine radiating ribs. This species has been confused with P. discus Conrad. Arnold in his paper ‘‘The Tertiary and Quaternary Pectens of California’’ (Prof. Paper U.S. G. 8., no. 47) plate XXVIJ, fig. 1, figures under the name of P. discus a very good specimen of P. raymondi, n. sp. This came from the San Pablo near the town of Walnut Creek. Figure 2 on the same plate, also listed as P. discus Conrad, shows a rather broken specimen of a species which is common in the Monterey shale in the southern part of the state. This form is referred to by Dall (Trans. Wagner Free Inst. Sci., vol. 3, pts. 3-4, pp. 704, 705) as P. discus Conrad. The writer has some very good specimens of this last form from the Monterey shale. It is very different from P. raymondi, being equivalved, thinner and shows a distinct fine imbri- cated concentric sculpturing. It is somewhat similar to P. pabloensis Conrad in that sometimes a narrow riblet is seen in the interspace of the radiating ribs and there is a tendeney for the major radiating ribs to divide dichotomously, also they become finer towards the dorsal margins of the shell. Neither P. raymondi, n. sp., nor the Monterey species referred to above, agrees with the original description or picture of P. discus Conrad. The type of P. discus Conrad evidently came from the Lower Miocene, Vaqueros or Monterey. Conrad’s meagre description and his picture agree fairly well with P. andersoni Arnold, a characteristic Monterey or Temblor form. It therefore seems very probable that P. andersoni Arnold should be considered as a synonym of P. discus Conrad. Before the change is made, however, good material should be obtained from the section from which the type of P. discus Conrad was obtained. Therefore the writer for the present accepts Dall’s determination of P. discus, leaving for the present P. andersoni as a legitimate species. P. raymondi, n.sp., may easily be, and has many times been, mis- taken for P. andersoni Arnold. Both species belong to the subgenus Pecten, having the left valve convex and the right valve flat. P. ray- mondi, n.sp., differs from P. andersoni Arnold in the following re- spects: It has a larger number of radiating ribs; the interspaces are not so wide. On P. andersoni Arnold the radiating ribs of the left valve are much narrower at the top than at the bottom, the top of the rib tending to be subangulate. On P. raymondi, n.sp., the radiating 452 University of California Publications in Geology [ Vou. 8 ya ribs of the left valve are broadly rounded to flat-topped. The radiating ribs of the flat right valve of P. andersoni Arnold are distinctly rounded, but not as narrow-topped as those of the left valve. The radiating ribs of the right valve of P. raymondi are broad and usually flat-topped. P. andersoni Arnold appears to be characteristic of the Monterey or Temblor Horizon. The writer has never seen it in the Upper Miocene. P. raymondi, n.sp., is a common and a very characteristic species of the Upper Miocene. It is very common in the San Pablo of Middle California and also in the Seutella breweriana zone. It is also very common in the ‘‘Santa Margarita’’ in the southern part of the state. Named in honor of Professor W. J. Raymond of the University of California. Dimensions —Large specimen figured, height, 50mm.; length, 50mm.; diameter, 7 mm. Occurrence —University of California localities 1942, 1947, 1946, 1478, 136, ete.; also from the Seutella breweriana zone in Middle California and from the Santa Margarita of the southern part of the state. PECTEN (CHLAMYS) PABLOENSIS Conrad Plate 47, figure 8; plate 48, figure 2 1857 Pecten pabloensis Conrad, Pac. R. R. Rept., vol. 6, pt. 2, 1857, pp. 71, pl. 3, fig. 14. 1888 Pecten pabloensis Conrad.? Cooper, 7th Ann. Rept. Calif. State Mineral., 1888, p. 258. 1898 Pecten (? Plagioctinium) pabloensis Dall. Trans. Wagner Free Inst. Sci., vol. 3, pt. 4, 1898, p. 708. 1906 Pecten pabloensis Conrad. Arnold, Prof. Paper U. 8. G. 8. no. 47, p- 88, pl. XX VII, figs. 6, 6a (not fig. 5 and 5a or 7). 1909 Pecten pabloensis Conrad. Weaver, Uniy. Calif. Publ. Bull., Dept. Geol., vol. 5, no. 6, p. 262. 1912 Pecten pabloensis Conrad. Smith, Proe. Calif. Acad. Sci., 4th series, vol. IIT. Shell thin, medium in size, nearly equilateral, inequivalved; height about equal to width; apical angle averaging about 90°; hinge line about half the length of the shell; dorsal edges gently concave; pos- — terior dorsal edge longer than anterior dorsal edge; anterior ears shghtly longer than posterior ears. Right valve sculptured by seven- teen to nineteen low, rounding ribs with interspaces averaging a little wider than the top ribs; a fine narrow riblet in each interspace. Sur- face also sculptured by fine, imbrieated, concentric lines which, when 1915] Clark: Fauna of the San Pablo Group 453 the valves have not been too much eroded, tend to come to a point on the tops of the ribs and riblets. The larger ribbing becomes finer toward the dorsal margins while the riblets become more prominent, the last few ribs not being distinguishable from the riblets; sometimes there are six or seven or even more of these finer undifferentiated ribs near the margins. The ribbing on the larger specimens is broader and flatter and tends to be dichotomous toward the ventral edges; this splitting of the ribs first makes its appearance toward the outer edges, but on the larger shells all the ribs may be dichotomized ventrally ; in some cases the riblets also are dichotomous. Anterior ear deeply notched, sculptured by four to six fairly prominent radiating ribs. Margin of posterior ear straight, sculptured by three to six medium fine, radiating ribs. Left valve usually more ventricose than right valve; sculptured by seventeen to nineteen low, rounded radiating ribs with the interspaces nearly twice as wide as the tops of the ribs; a fine narrow riblet in each interspace as on right valve; ribbing finer toward dorsal margins, becoming indistinguishable from riblets; the larger ribs as in the case of the right valve tend to become dichotomous and the riblets also tend to split. Surface imbricated as on right valve. Anterior ear slightly notched, sculptured by four to six medium fine radiating ribs; posterior ear with about equal number of ribs, posterior edge straight. Ligamental groove fairly heavy. Resilifer small. Adductor muscle impression large. P. pabloensis is found associated with P. bilineatus, P. holwayi and P. crassicardo. It has been confused many times with P. bil- ineatus and P. raymondi. In Professional Paper 47, pl. X XVII, fig. 5, Arnold has figured the left valve of this species. Figure 6 of the same plate represents a specimen of P. bilineatus, while figure 7 appears to represent the left valve of P. raymondi, un. sp. Dimensions.—Specimen figured on plate 47, figure 8. Height, 32 mm.; leneth, 39mm.; length of hinge, 22mm.; length of anterior dorsal edge, about 18 mm.; length of posterior dorsal edge about 22 mm.; diameter of right valve, about 3 mm. Occurrence—On San Pablo Bay in the Upper San Pablo group, University of California loealities 1632, 1613, 1614 and 1615; also, on the north side of Mount Diablo in the Upper San Pablo, University of California locality 1891. 454 University of California Publications in Geology [ Vou. 8 PECTEN (PALLIUM) HOLWAYI, n. sp. Plate 47, figure 5 Shell large, equilateral; posterior, anterior, and ventral margins strongly depressed; surface of shell with a marked step-like depres- sion, indicating a former depressed ventral margin, situated not quite one third the distance from the ventral edge to the beak. Surface sculptured by three heavy rounding ribs; these ribs are very promi- nent between the step-like depression and the ventral depressed mar- ein, but very faint and almost disappearing between the step and the beak. Surface also sculptured by fine, regular, radial striae or riblets, which cover both the interspaces and the ribs, and by fine imbricate concentric lines. Shell feebly lirate internally, the hrations being most prominent on the depressed area along the ventral edge. Adductor muscle scar prominent. Named in honor of Professor R. 8. Holway, Associate Professor of Physical Geography at the University of California. Dimensions —Height of shell, 85mm.; length of shell, 90mm.; ereatest diameter of valve, about 24 mm. Occurrence.—In Pecten beds of the Upper San Pablo group on San Pablo Bay to the south of the town of Rodeo, University of Cali- fornia locality 1632. PECTEN (PATINOPECTEN) WEAVEBRI, n.sp. Plate 45, figures 1 and 2 Shell discoidal, broader than high, equilateral, nearly equivalved; apical angle about 90°; dorsal edges gently concave; hinge line about half the length of the shell. Right valve sculptured by about four- teen low, broad-topped, squarish ribs, the interspaces between which are flat-bottomed and about as wide as the tops of the ribs. Surface concentrically sculptured by rather coarse, somewhat irregular incre- mental lines. Anterior ear slightly longer than posterior, deeply notched, sculptured by three medium coarse, radiating ribs. Posterior ear marked by two or three faint radiating riblets. Left valve seulp- tured by fourteen fairly prominent, rounded, radiating ribs with interspaces about equal to the width of the ribs; the ribs next to the dorsal edges are not so prominent as the others. Surface also covered by fine, sharp, incremental lines. Anterior and posterior ears each marked by three medium fine, radiating riblets; anterior edge of an- terior ear slightly notched. 1915] Clark: Fauna of the San Pablo Group 455 The differences in the sculpturing on the two valves is quite notice- able; the left valve, with fairly prominent rounded ribs and the sharp incremental lines, contrasts quite strongly with the right valve, with its low, squarish ribs and coarser incremental lines. Named in honor of Professor Charles E. Weaver of the University of Washington. Dimensions.—Of left valve, plate 45, figure 2. Height, 34 mm.; length, 36 mm. Occurrence—F rom the basal beds of the San Pablo group on San Pablo Bay, University of California localities 1141 and 401. MYTILUS MERRIAMI, n. sp. Plate 48, figures 7 and 8 Shell thick, very ventricose. Beaks heavy, bluntly pointed. Hinge plate below the beaks very heavy. Base sometimes straight, sometimes gently concave. Posterior edge angulated, the point of angulation being situated anterior to the middle. Posterior extremity evenly rounded. Surface of shell covered by irregular coarse incremental undulations. Highest point of convexity of surface anterior to the middle of the valve; anterior slope high and nearly perpendicular ; posterior slope steep, dropping at an angle of nearly 30° as measured at the point of angulation on the posterior edge; to the rear of this point the shell is not so convex; no teeth on thickened hinge plate. Thickened area below the beaks obscurely grooved; deep elongate an- terior adductor muscle sear just below the thickened hinge plate. M. merriami, n.sp., differs from M. coalingensis Arnold and the variety of that species from the San Pablo, in that the slopes are more ventricose; the posterior slope is steeper; the valves do not flatten out toward the base so markedly; it lacks the deep pit which lies im- mediately below the cardinal hinge plate on the other two forms. M. merriami, n.sp., differs from M. perrini, n.sp., also from the Upper San Pablo Group, in being larger, in having a heavier hinge plate; the valves are higher and more convex and the anterior and dorsal slopes are much steeper. M. merriami, n. sp., differs from M. mathewsonii Gabb, a Lower Miocene form, as follows: On M. merriami, n. sp., the base is straight, on M. mathewsonivi Gabb it is curved, on the former the highest point of convexity of the surface is nearer the median line than on the latter; also the posterior extremity is not so broad. 456 University of California Publications in Geology [ VoL. 8 M. expansus Arnold, deseribed by Arnold as a variety of M. mathewsonii Gabb, is somewhat similar in outline to M. merriami, n. sp., but differs in being less convex; the posterior slope is less steep and the posterior margin is not angulated as is the case of M. merriami, n. sp.; the latter also lacks the radial striations seen on M. expansus. It would seem to the writer that Arnold’s M. mathewsonw var. expansus should be classed as a true species, not a variety. M. expansus Arnold belongs to the section Hormomya Moreh according to Dall’s classification. M. mathewsonii Gabb belongs to the section Mytilus. It does not appear to be radially striated as stated by Dall in his dis- cussion of the species of Mytilus of the Pacific Coast (Transactions of the Wagner Free Institute of Science, vol. 3, pt. 4, p. 789, 1898). Dimensions —Greatest antero-posterior diameter, about 104 mm.; greatest width as measured at right angles to the base, about 55 mm.; height of the depressed anterior margin, about 42 mm. Occurrence—F rom the upper beds of the Upper San Pablo Group on the south side of Mount Diablo, University of California locality 118. Named in honor of Professor J. C. Merriam, Professor of Palae- ontology at the University of California. MYTILUS PERRINI, n. sp. Plate 42, figures 5 and 6 Shell medium in size, somewhat variable in outline, elongate sub- ovate; beaks subacute, slightly twisted; base straight or slightly con- cave. Posterior cardinal angle as a rule slightly anterior to the middle of the elongate axis, the angle being obscured on some of the larger Specimens, the margin posterior to the point of angulation being nearly straight and parallel or slightly diverging from the anterior edge. Ventral edge broadly rounded to subtruneate. Surface of shell covered by heavy irregular undulations with finer ineremental lines. Anterior slope of surface fairly abrupt; posterior slope gentle. There is a tendency for the surface of the shell to be depressed and flattened just in front of the posterior dorsal edge. Hinge plate heavy below the beak; on some specimens the thickened hinge plate resembles somewhat the myaphoric septum of a Septifer or Dreissensia; the anterior edge of the smaller specimens is denticulate immediately below the beaks; on the smaller specimen figured at least ten of these 1915] Clark: Fauna of the San Pablo Group 457 minute teeth may be counted. Ligamental groove broad and fairly heavy ; anterior adductor sear long and narrow. This species is very closely allied to WM. eduius Linn.; it differs in having heavier lines of growth; the basal margin and posterior mar- gin posterior to the point of angulation are nearly parallel or slightly diverging while on M. edulus they are converging; the hinge plate is very much heavier and when there are teeth on the anterior margin, they are finer and more numerous; the ligamental groove also appears to be somewhat heavier. M. perrini, n. sp., differs from M. mathewsonii Gabb in that the latter is a larger form; the general outlines of the two shells are different; the highest point of convexity on the surface of M. mathew- sonii Gabb is near the middle of the shell, on MW. perrini it is in front of the middle; further, the posterior slopes of MW. mathewsonu Gabb are steeper than on WM. perrini. The writer has been unable to get a good specimen of the hinge of M. mathewsoni. M. perrini, n. sp., resembles M. californicus Conrad in the fairly coarse concentric undulations; it lacks the heavy radial sculpture of M. californicus; the hinge plate and outline are also quite different. M. perrini differs from M. expansus Arnold (listed by Arnold as M. mathewsonii Gabb var. expansus, n. var.) in that it is a smaller form; the posterior dorsal margin is shorter; the surface lacks the fine radiating striae seen on M. expansus Arnold. In other respects the two forms seem to be quite similar; both have a broad, subtruneate ventral edge and usually a straight base, the anterior slope of the surface being quite abrupt, with the highest point of convexity well in front of the middle of the shell. Dimensions—Type specimen: greatest anteroposterior diameter about 57 mm.; greatest width measured at right angles to base, 25 mm Occurrence-—Upper San Pablo Group on San Pablo Bay, Univer- sity of California locality 1617. Named in honor of Professor James Perrin Smith, Professor of Palaeontology at Leland Stanford Junior University. MYTILUS (MYTILOCONCHA) TRAMPASENSIS, n. sp. Plate 42, figures 2 and 3 Shell medium to large, low, slender; beaks acute, not twisted; base nearly straight, on some specimens gently concave. Cardinal angle near the middle of the elongate axis. Posterior end evenly rounded: 458 University of California Publications in Geology [ Vou. 8 anterior slope steep; surface of shell posterior to the steep anterior slope slightly convex, with a very gentle posterior slope. Surface smooth except for fine incremental lines of growth. Hinge plate below the beaks heavy, with a deep groove anterior to the ligamental eroove. This species differs from Mytilus coalingensis Arnold in being more slender, not so broad posteriorly ; the beaks are not twisted; the surface is not so high or convex, the anterior slope not being so high but possibly steeper. Occurrence.--In the Upper San Pablo Group on Las Trampas Ridge and Rocky Ridge near southeast corner of Concord Sheet, Uni- versity of California localities 38, 39, 1237. MODIOLUS GABBI, n. sp. Plate 48, figure 1 Modiolus multiradiatus Gabb (in part), Pal. Calif., vol. 2, p. 30, not pl. 8. Modiolus multiradiatus Gabb (Smith), Proe. Calif. Acad. Sci., 4th ser., vol. II, p. 172. Shell medium to large, elongate, anterior end extending only slightly beyond the beak. Posterior dorsal edge subangulate posterior to the mid-length of the valve. Base nearly straight with a tendeney to concavity; posterior end evenly rounded. Surface sculptured by rather broad, flat-topped, dichotomous ribbing, except for an elongate, smooth, subtriangular space above the base near the anterior end; the dichotomous ribbing is more marked toward the posterior margin, while anteriorly the ribs are split only at their lower ends; interspaces slightly narrower than the tops of the ribs. Surface quite strongly convex, usually with a well-defined ridge marking the line of greater convexity extending from the beak toward the basal side of the pos- terior extremity; on the larger specimens this ridge is not so pro- nounced, the surface being more evenly rounded. This species has heretofore been known as Modiolus multiradiatus Gabb, which Gabb reported from two localities, San Emideo ranch, west of Fort Tejon, and the Miocene of Contra Costa County. The type specimen without doubt came from San Emideo ranch. Some of Gabb’s original material from this locality is in the collections of the Department of Palaeontology at the University of California. The form from San Emideo ranch differs from the one in the Upper Mio- 1915] Clark: Fauna of the San Pablo Group 459 eene of Middle California both in outline and in seulpturing. The radial ribbing on WM. multiradiatus is much finer and closer together than on M. gabbi; also, on the former the anterior end extends much further beyond the beak than on the latter. MW. multiradiatus is found in the Lower Miocene (Vaqueros) of Stone Cafon, Monterey County, and it is probably characteristic of that horizon. Dimensions.—Greatest antero-posterior diameter, 71 mm.; width of shell as measured from point of angulation, 30 mm. Occurrence.—A very common form in the lower and upper San Pablo Group; also found in the Seutella breweriana zone. CYRENA (CORBICULA) CALIFORNICA Gabb Plate 56, figure 2 Gabb in speaking of this species says: This species is the most variable in outline of any fossil I have seen in California except the oysters and similar shells. No two specimens have the same shape and by selecting a suitable series, differences enough could be found to make three or four species, sufficiently distinct on paper. The large number of specimens, however, at my disposal, show conclusively that all belong to but one species. C. californica is very abundant at one horizon near the top of the San Pablo Series on San Pablo Bay. Here it is just as variable as at Kirker Pass, whence it was first described; it is associated everywhere with genera that may have a brackish-water habitat. On San Pablo Bay it is associated with the following species: Mytilus perrini, n. sp., Bittium pabloensis, n. sp., Cerithiwm rodeoensis, n. sp., Mya dickersoni, n.sp., and Macoma pabloensis, n. sp. At Kirker Pass C. californica is associated with Littorina pittsburgensis and Trophon ponderosum. Occurrence.—Upper San Pablo, University of California localities 1617, 1942, 1482, 59, 147, 1198. DOSINIA (DOSINELLA) ARNOLDI, n. sp. Plate 51, figures 1 and 2 Shell large, tumid; beaks fairly prominent; base broad; anterior extremity rather strongly produced and regularly rounded. Posterior dorsal edge long and gently arcuate; anterior dorsal edge long for this genus, nearly straight, except just below the beak, where it is ‘slightly concave; ventral edge regular and rather strongly rounded; posterior extremity subangulate. Lunule large, deeply impressed. 460 University of California Publications in Geology [ VoL. 8 Posterior dorsal margin slightly flattened into an escutcheon-lke area, which is more prominent toward the base than in the vicinity of the beaks. Surface sculptured by numerous, somewhat irregular, con- centric lines. Hinge plate of left valve broad with three well devel- oped cardinals; posterior cardinal elongated but not prominent, with small contiguous area of hinge plate roughened; anterior cardinal rather thin and high; anterior lateral strongly developed for this genus. The writer was not able to get a good specimen of the hinge of the right valve. Pallial sinus elongate, subacute. Adductor muscle impressions strong, especially the anterior one. figure 13. [566] UNIV. CALIF. PUBL. BULL. DEPT. GEOL. [CLARK] VOL. 8, PL. 68 Fig. 1. EXPLANATION OF PLATE 69 Cerithium rodeoensis, n. sp. Altitude, 17 mm. Neither of the speci- mens figured shows the longitudinal ribbing usually seen on the whorls of the spire. Natural size. 7 9 Fig. 2. Fig. 3. Fig. 4. Murex (Ocinebra) packardi, nu. sp. Altitude, 41 mm. Natural size. Olivella pedroana Conrad. Altitude, 15 mm. Natural size. Natice (Euspira) kirkensis, n. sp. A very common species in the Lower San Pablo; also found in the Scutella breweriana zone. Altitude, 32 mm. Natural size. Fig. 5. size. Fig. 6. Fig. 7. size. Fig. 8. ural size. Fig. 9. Fig. 10. ural size. Fig. 11. Turris kirkensis, nu. sp. Altitude, 13 mm. Enlarged twice natural Turris kirkensis, n. sp. Enlarged twice natural size. Turris kirkensis, n. sp. Altitude, 10 mm. Enlarged twice natural Columbella kirkensis, n. sp. Altitude, 10 mm. Enlarged twice nat- Natice (Euspira).kirkensis, n. sp. Altitude, 35 mm. Cerithium rodeoensis, n. sp. Altitude, 15 mm. Enlarged twice nat- Murex (Ocinebra) packardi, n. sp. Altitude, 31 mm. Natural size. [568] UNIV. CALIF. PUBL. BULL DEPT. GEOL. [CLARK] VOL. 8, PL. 69 a EXPLANATION OF PLATE 70 All figures approximately natural size Crepidula pabloensis, n. sp. Showing concave deck. Crepidula pabloensis, n. sp. Altitude, 22 mm. Crepidula pabloensis, n. sp. Altitude, 20 mm. Cerithiopsis, sp. A. Cerithiopsis, sp. A. Crepidula adunca Sowerby. Altitude, 10 mm. Crepidula pabloensis, n. sp. Type. Altitude, 20 mm. Calyptraea martini, n. sp. Altitude, 28 mm. Calyptraea diabloensis, n. sp. Altitude, about 25 mm. UNIV, CALIF. PUBL. BULL. DEPT. GEOL. [CLARK] VOL. 8, PL. 70 EXPLANATION OF PLATE 71 Map showing distribution of San Pablo Group and portion of Group in the region of San Pablo Bay. [572] UNIV. CALIF, PUBL. BULL. DEPT. GEOL. [CLARK] VOL. 8, PL. 7I ETpt Pinole Tuff [fifsell] San Pablo Monterey ETfm=| Sandstones ETms4 First Shale za Bt -)- O- : Ses = Mn SONI seat Lt TK Eocene ALAR) (| and ih ; I Cretaceous FAL ’ : a HIN Lines WN ———= — } EIN \ UTR Zs \ A ‘\ Tk Z\ \ = lf = —~_ \ pe a. Si] QE Clark, Bruce Lawrence 747 Fauna of the San Pablo C204 group of middle California Geology IGS PLEASE DO NOT R CARDS ROM THIS POCKET es UNIVERSITY OF TORONTO LIBRARY ee Colenmaii Library Department of Geology Univer ity of Toronto a