Page 44 - Land Snails of New Mexico

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Ridge.Theprecariousnatureofthepopulationwasemphasized InarevisionofsomeNorthAmericanbulimulids,Pratt
in the title of our 1974 paper: "Gastropods of Howells Ridge, GrantCo.,New Mexico;afaunaintheprocessofextinction?".
(1974:24-25) elevated the subgenus Rabdotus to generic status. He alsosynonymizedB.pasonisPilsbrywithB.durangoanus (von Martens), with type locality in Durango, México. He relegateddurangoanustosubspecificstatusunderB.dealbatus, noting that the two kinds intergraded in places in Texas and México. In addition, he deemed the subspecies neomexicanus as not sufficiently different from the nominal subspecies to require recognition.Thus,inthepointofview ofPratt'sreport,thetwo kinds of bulimulids in the San Andres, Sacramento, and Guadalupe Mountains become Rabdotus dealbatus dealbatus (Say)andR.dealbatusdurangoanus(vonMartens).This creates an unusual situation in which two subspecies of R.
Genus Coelostemma
Coelostemma (Goniapex) pyrgonasta F. G. Thompson, 1988. Bulletin of the Florida State Museum, Biological Sciences, 33:92 Figs. 12-14. T.L.: Bishops Cap Mountain,
DoñaAnaCo.,New Mexico.(bishoptubeshell)
Thompson(1988)placedthisspeciesinagenusformerly known in México, but new to the United States. The species is endemic to Bishops Cap Mountain, a pyramidal peak located betweenLasCrucesinDoñaAnaCo.,NewMexico,andEl Paso,Texas.Itcanbeseenasasalientfeatureafewmilestothe eastofInterstateHighway 10. Specimens ofC. pyrgonasta have been found in the eastern, western, and northern parts of the mountain; thus they seem to be distributed widely in this small range. Bishops Cap isa low, arid mountain, reaching 5,419 ftin elevation. T h e vegetation consists of xeric-adapted species of the ChihuahuanDesert,predominantlycreosotebush.Specimensof this species were found under limestone blocks below cliffs. MetcalfwaswithDr.FredG.Thompsonwhenthetypeswere collected and learned that this urocoptid apparently prefers to live under large stones, which required his strength and skill to lift. Living specimens were scattered in occurrence, not concentrated in small pockets as was the case with H. metcalfi on Howells Ridge, discussed above. The area occupied by C. pyrogonastaisgreaterthanthatoccupiedby H. metcalfi,butis nevertheless quite small--only about 3 or 4 square miles.
dealbatus coexist in the three ranges without intergradation, whichisanawkward,althoughnotimpossible,stateofaffairs. Because of a seeming lack of detailed information about the supposed intergradation between the durangoanus and dealbatus forms in México, w e will retain, conservatively, the nameusedbyPilsbryforthelargeforminNewMexico:R.d. neomexicanus, and treat R. durangoanus as a full species.
Family Bulimulidae Genus Rabdotus
Habitat--This subspecies is found only in areas of calcareous bedrock. It occurs widely in the San Andres Mountains south of the igneous-rock area in the Salinas Peak complex. However, in the extreme southern end of the range, it is replaced by R. durangoanus. It also occurs to the east in the Oscura Mountains. In the Sacramento Mountains, R. d. neomexicanus occurs on the eastern slope and up to about 7,650 ft in the central part of the range. It is replaced by R.
Rabdotus dealbatus neomexicanus (H. A. Pilsbry, 1946, as Bulimulus). Academy of Natural Sciences of Philadelphia Monograph, 3(II)1:13, Fig. 4:e,f T.L.: at Burke's (=Burke) Spring, west slope of San Andreas (=Andres) Mountains, Doña Ana Co., New Mexico. (whitewashed rabdotus)
durangoanus on the southwestern slopes of the range, as in D o g Canyon. Similarly, in the Guadalupe Mountains, the larger R. d. neomexicanus is more widespread and R. durangoanus is restricted to slopes of the western part of the range.
Taxonomically, the situation with this species is complex in the area treated here. Pilsbry (1946:13,19) considered that two bulimulid species existed in southern New Mexico: 1) Bulimulus pasonis Pilsbry, with type locality in the Franklin Mountains, Texas, which he recognized also from the SacramentoandGuadalupeMountainsofsouthernNew Mexico and adjacentTexas, and 2) Bulimulus dealbatus neomexicanus Pilsbry, a subspecies of the widespread species, B. dealbatus, which ranges from Kansas southward into México. Pilsbry designated the type locality of neomexicanus as Burke's Spring (environs) in the San Andres Mountains and reported italso from the Sacramento and Guadalupe Mountains. A s represented in the above mountain ranges, shells of the two taxa differ greatly, B. d. neomexicanus being more robust and thick shelled,reachingsome30mm inheightand19mm inwidth,
Paleontology--Fossil specimens of this species have been
whereas B. pasonis is a more gracile form, reaching only about 17mm inheightand9mm inwidth.
Rabdotus durangoanus (E. von Martens, 1893, as Bulimulus). Biologia Centrali-Americana, p. 246, Pl. 15, Fig. 11, 11a. T.L.: Villa Lerdo, State of Durango, México.
GeneralandNewMexicoDistribution--ThespeciesR. dealbatusisfoundinthesouth-centralUnitedStates:eastto
Alabama, Tennessee, and Kentucky, north to Kansas and
Missouri,westtoNewMexico,anditalsooccursinnorthern
México. The subspecies, R. d. neomexicanus, as recognized
here,isrestrictedtosouthernNew Mexico andtheGuadalupe
Mountains of Texas. It might be sought in the Delaware
MountainsofTexas,aswell.InNew Mexico,thissubspeciesis
found in the San Andres, Sacramento, and Guadalupe Mountains.
found at several localities in Pleistocene sediments along
canyons in the Sacramento Mountains. They closely resemble
those in populations inhabiting the mountains today, indicating
that the species has been there for a long period of time. Slightly
to the west of the presently k n o w n range of the species, Metcalf
(1967:47) reported a few poorly preserved specimens of a Rabdotus from Pleistocene sediments in the foothills of the
RobledoMountains,northofLasCruces,DoñaAnaCo.,New Mexico. Tentatively, these specimens were assigned to R. dealbatus. ,