Page 83 - Land Snails of New Mexico

chriacorummightbearibbedhelicinid.A shellinNMMNHlot
PLS-20-92 (uncataloged) conforms well with illustrations of
cotypes of H. adipis in White (1886:Pl. 5) and Hartman
(1981a:Fig.1).However,thesizeoftheNMMNH specimen
(12.0mm widthand8.5-mmheight)isconsiderablygreaterthan
thatindicatedforspecimensdepictedbyWhiteandHartman considerableresemblancetoshellsofR.nacimientensis.This (with5.0-mmwidthand3.0-mmheightforthetype).Thislarger
size accords well with Solem's suggestion that this species appertains to the Helminthoglyptidae.
suggests that a single species or species complex of Radiocentrum may have been widespread in the Cordilleran region at a time in the Paleocene.
The urocoptid snail Holospira grangeri Cockerell, 1914, is well represented in collections from the Nacimiento Formation includingthoserecentlymadebytheNewMexicoMuseumof Natural History ( N M M N H Nos. P-15694, P-15695, and P
In summary, the Paleocene record seems to present good evidence for the presence of the families Urocoptidae, Oreohelicidae, and Polygyridae in northwestern N e w Mexico and suggests the possible occurrence of members of the Helicinidae and Helminthoglyptidae.
15697).
In his description of Polygyra petrochlora, Cockerell
Eocene records are few and seem to include only specimens
(1914:103) had available only four shells, these from a greenish facies of the Nacimiento Formation, which Cockerell pointed out as differing in colorfrom beds in which other mollusks had been found in the formation. The shells were fragmentary and Cockerell placed them in the genus Polygyra with some hesitancy. The thickened, reflected lip figured in Cockerell's Plate 8, Fig. 7, suggests a polygyrid. T h e dimensions of the type (20-mm width and 14-mm height)aresimilartothoseoflarger species of modern Ashmunella of New Mexico. Polygyra petrochlora may well be an early Ashmunella, as this seems reasonable on zoogeographic grounds. However, as pointed out by Cockerell (1914:101), itis not always possible to distinguish between the two genera on the basis of shells alone. Additional, better-preserved specimens of this species are m u c h needed.
ofacamaenidsnailofthegenusHodopoeus.Thisgenuswas
Helix nacimientensis White, 1886, was allocated to the
Clearly, the early Tertiary land-snail fauna must have been much richer in taxa than the above meager records would indicate. Itwould be informative to have extensive early Tertiary records from nearby states. Roth (1984) and Roth and M e g a w (1989) have reported faunas from western Texas and central Chihuahua,México.However,ArizonaandColorado,likeNew Mexico,haveadearthofrecords.Thisisunfortunate,because Arizona was likely a source area of land snails colonizing N e w Mexico upon recession of the epeiric sea, and Colorado was likely a source of species inhabiting the Rocky Mountains of northern N e w Mexico.
genus Oreohelix, subgenus Radiocentrum by Cockerell
(1914:103). Radiocentrum has since been elevated to generic status. Radiocentrum nacimientensis is the most common
PaleocenespeciescontainedincollectionsoftheNew Mexico
Museum of Natural History. A number of well-preserved
specimens have been acquired, some with whitish shell material
still i n t a c t a n d s h o w i n g s c u l p t u r e . I n s o m e o f t h e s e s p e c i m e n s ,
the typical radial striae on the apical whorls of specimens of
Radiocentrumareobservable,asinNMMNHNos.P-15678,P Thereare,however,recordsfromUtah,Wyoming,and 15786, and P-16324. The species is robust. White's (1886)
holotypehadawidthof42mm, andseveralspecimensinthe NMMNH collectionsarearound40mm inwidth.Widthsfor7
Montana, which allow inferences about the nature of the early Tertiary fauna of the present central Rocky Mountain region. S o m e publications of significance to achieving an understanding of early Tertiary faunas in the greater region include the
specimens from Lot PLS-20-92 (uncataloged) ranged from 28.0
to41.9mmwithameanof33.5mm.Asisthecaseinmany following,arrangedfromUtaheastwardintheMontana
oreohelicids, younger shells are depressed, flattened dorsally, and tend to be carinate peripherally. A s whorls are added on oldershells,theperipherybecomes progressivelymore angular (by 25-30mm inwidth) and then more rounded (by 35-40 mm). Cockerell (1914:103) indicated that the type of his n e w variety steini had a width of 32.5-mm, and differed from typical nacimientensis in having a more angular shell. This peripheral angularity seems, as noted above, to be characteristic of shells in the size range of the type of steini. Hartman (1981a:945) noted thatthetypeofsteiniwas thespecimenillustratedby Cockerell (1914:Pl.8,Figs 3and4).AccordingtoRoth(1986:265),D. W. TaylorhadsuggestedthatO. n.steiniwas a"New speciesof Camaenidae." However, Cockerell'sPl.8,Fig.4 clearlyseems
W y o m i n g region, then southward to Texas and Chihuahua: 1) LaRocque (1960), Paleocene and Eocene strata of Flagstaff Formation, centralUtah; 2) Hanley (1976), Eocene Green River and Wasatch Formations, southwestern Wyoming and northwestern Colorado, 3) McKenna, Robinson, and Taylor (1962) and Dorr (1969), Eocene, central western Wyoming; 4) Russell (1931), Eocene, northwestern Wyoming; 5) Roth (1986), Eocene-Oligocene, Bozeman Group, southwestern Montana and summary ofregional records; 6) Evanoff and Roth (1992), Evanoff, Prothero, and Lander (1992), Eocene-Early Oligocene,WhiteRiverFormation,east-centralWyoming,7) Roth (1984), Eocene-Oligocene, Vieja Group, Trans-Pecos Texas; 8) Roth and Megaw (1989); Megaw, McDowell and Roth (1994), upper Eocene strata, central Chihuahua, México.
to show the apical sculpture of a Radiocentrum.
As pointed out by Cockerell (1914:103), there is much similarity between shells of Radiocentrum nacimientensis and ofR.megarcheCockerellandHenderson,1912,fromWyoming. TheillustrationsofR.megarcheinRussell(1931:Pl.3)show
discussed by Solem (1978), and comprises two named species:
H. hesperarche (Cockerell, 1914) and H. crassus Pilsbry and
Cockerell, 1945. The typelocalityofneitherspeciesisknown,
butmaybeinNewMexicoorwesternTexas.InNewMexico,
specimens of a Hodopoeus have been collected from the Regina MemberoftheSanJoseFormationinnorthwesternNew Mexico
(NMMNHP-11375) andfromthePalmParkFormationinthe south-centralpartofthestate(UTEP 12,532).SmithandLucas (1991:35) considered mammalian fossils from the Regina Member tobe ofearlyEocene (Wasatchian) age and suggested anapproximateageforthemof53Ma.
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