foI'nintions. St>'apa>'o?7228 (E2201>2pha?228) a?a8Ii'c22222$ u. sp. occiiI's ln nil tllree formations„nnd Amphi8capha (Cyl>'c2'osca?>ha) g>ac?a, n. sp. is present in the latter two. Finally, 3lo222?o>iia'~ 2.c?oba, n. sp. occurs in the uunainecl formation, is tentatively identified in collec- tions froni the Siksikpuk forniation, ancl mny be pres- ent, in the Sndlerochit formation.

USOS locality 14174, assignecl to the Siksikpuk forniation on the basis of rock type, is atypical. The collection consists of two specimens of Cr?ab>'oc2'2>g227222>2, ((~?ab> oc2'2>g22722m) sp. and one specimen of T>eponpis'a (Tn'po8p22'a) sp. Except for one questionable occur- rence, T>'epospi>'a is unknown in Perlnian faunas else- where in the world. Furthermore, the specimens of G?abroc22>g227222n, cli8er from Perniian species known froni the southwestern Uuitecl States nncl other well- lcnown areas of Pernrian exposures. It niay be, that this collection is actually of Pennsylvanian nge. More fielclwork in northern Alaska ancl nclclitional collec.- tions are needecl to confirni the presence of Pennsyl- v'11111111 I'OCkS.

Iknown 1 niiges 0 f tlie nlore significan species nl e shown in figiiiie 95.

ECOLOGICAL AND PALEOGEOGRAPHICAL DATA

Representatives of five superfnniilies — euomphala- eeans, plntycerataceans, pleurotomariacenns, nerita- cenns„nncl bellerophontnceans, in that orcler of nbim- clnnce — coniprise virtunlly nll the gnstropocls stuclied. The groups are represented by nearly equal nunibers of speciniens, with the euomphalncenus being perhaps half again as abunclniit ns the bellerophontaceans. Although many of the pleurotoniarincenns are poorly preservecl, this group hns consiclernbly niore generic cliversity thnu the others.

Incliviclunl collections show little taxonomic variety. Less thnu 10 percent, of the collections contain niore than three tnxa. This lack of clivcrsifiicntion inay re- flect the snnill nniount of collecting or it niny, in part, refiect n tiine of unfavornble or relntively uniform en- vironiuent. For exnniple, fossils of Lower Mississip- pinu strata of the western Unitecl States have been eollectecl for nearly 100 years, but, relatively few gas- tropocls nre knosvn. It coulcl be more. tlian coincidence thnt, both regions were the, sites of preclominantly elas- tic liniestone deposition during the late Paleozoic.

Ecologic ancl pnleogeographic inferences clrawn froiii this stucly are listed below. Further work is neeclecl before the generalizations can be appliecl to upper Paleozoic gastropocls froui other regions. These inferences involve examination of other fossil groups in the late Paleozoic faunas of the region. Docu- nientation of some of the stateiuents nuist necessarily

nwnit the publication of research by other specialists.

1. P?atyce>aa commonly occurs here in crinoidal lime- stone. This partially supports the hypothesis con- ceniing life relationships of platyceratids on pelma- tozoan calyxes (Bowsher, 1955).

o. In the Lower Mississippian where P?atycerow is

comnion, the associatecl gastropods show less vari- ety than in the Upper Mississippian. This sug- gests that areas of limestone deposition favorable for eiinoicls were unfavorable for most benthonic gast1'opocls.

.'3. >i't>n?>a>o?7222> occurs in limestone, sandstone, silt-

stone, and shale. This suggests that. species of this genus hncl consiclernble ecologic tolerance.

4. A.lthough large gastropods (an inch or mor.. in

height) are not confined to the coarse clastic facies, they are the only snails that have been collected froni rocks of t'his facies. These large gastropocls apparently livecl in a zone of heavy surf, the prob- able seclimentary depositional environment of the coarse clastic material. Sonic of the large shells occur in a siliceous conglomeratic niatrix contain- ing pebbles linlf an inch in cliameter.

5. Cephalopocls are rarely associated with the gastro- pocls; the. o groups occur together at only 6 lo".ali- ties. Corals ancl gnstropocls also appear to be ne.,rly nuitunlly exclusive, although cletails of coral clistri- bution have not, been published as yet. On the other hnncl, except, in the Eaticop8i>,suts2>rico>>>pta zone, gastropods are comnionly associatecl with nu- merous taxononiieally cliversifiecl brachiopocls. Ap- parently environments favorable for diversified brnchiopocl faunas n8orclecl optimum conclitions for abundant gastropods. Conversely, it seems that only cei<nin kincls of' gastropocls were able to live iu en- vironments well suited for corals ancl cephaloIods.

6. In the 7>Vaticopsia 822t22>ico>>>pta. zone, except for one

collection, fossil nsseniblages eoiisist, entirely of gas- tropods. There is no obvious explanation for this apparent exclusion of other fossil invertebrates.

Mississippian collections inclucle genera known to be common in the lower Carboniferous elsewher.. in the world. Heretofore they have not been reported from the Anierienn Arctic, and 1-nowleclge of their stratigraphic occurrence nnd geographic. clistribution fills nn importniit gap in our information ou paleo~eo- graphic clistribution. There is uo eviclence at the fnuiily level. ancl iuost probably none at the gei>eric level, tliat any of the groups is conspicuously pre.-eut or absent because of cold-water conditions. So far as cnii be inteiq>reted froin this stucly, a boreal marine invertebrate fauua clid not exist, in Mississippian time. The snail faunule is not particularly different, in gen-

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