Page 46 - Land Snails of New Mexico

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t h e M a g d a l e n a M o u n t a i n s , w e t o o k it n e a r t h e s u m m i t a t 1 0 , 2 8 0 ftin aspen forest. In the Sacramento-Sierra Blanca complex, w e collected italong canyons from 6,800 to 10,800ft.
Family Helicodiscidae Genus Helicodiscus
Subgenus Helicodiscus
Helicodiscus eigenmanni H. A. Pilsbry, 1900. The Nautilus, 14:41. T.L.: Beaver Cave, near San Marcos, Comal Co., Texas. (Mexican coil)
Helicodiscus eigenmanni bears considerable resemblance
to H. parallelus (Say, 1817). Bequaert and Miller (1973:152)
speculated that perhaps H. eigenmanni is only a southwestern
subspecies of H. parallelus. Pilsbry (1948:630), on the other
hand, championed a specific status for H. eigenmanni, noting:
"This fine species is easily recognized b y its large size, the shell
in all stages of growth being much more robust than H.
parallelus." Hubricht (1985:Maps 180,185) treated H.
eigenmanni and H. parallelus as distinctspecies and mapped
them as allopatric to each other. In Texas, he showed H.
eigenmanni as occurring in the central and western parts of the
state and H. paralellus only in some easternmost counties. To
the west, H. eigenmanni extends to Arizona and also into northern México.
NewMexicoDistributionandHabitat--InNewMexico, H. eigenmanniiswidespread,foundinmountainsthroughout the state, mainly in the Upper Sonoran and Transition Life Zones. Itoccurs in rocky areas in foothills and lower elevations of mountains, where there is some development of woodlands
sufficient to p r o d u c e leaf litter in w h i c h s p e c i m e n s c o m m o n l y are ensconced. It is found consistently in leaf litter from the elevations noted, but only in low numbers, typically comprising lessthan5% ofspecimenstakeninacollection.
Subgenus Hebetodiscus
andeasternpartsofNewMexico;itoccursmainlyinhilly country in both the Lower and Upper Sonoran Life Zones. Itis found commonly understones or in leaflitterbelow the scarp of theOgallalaCaprockineasternNew Mexico.Itoccursinrock talus along canyon walls and hillslopes of the arid lower mountains of the south-central and southwestern parts of the state. Helicodiscus singleyanus is a common fossil in both Pleistocene and Holocene deposits of river and arroyo floodplainsinsouthernNew Mexico.
Family Discidae Genus Discus
Discus whitneyi (W. Newcomb, 1864, as Helix). ProceedingsoftheCaliforniaAcademy ofSciences,3:118. T.L.: near Lake Tahoe, California. (forest disc)
Snails of this taxon long have been assigned to Discus cronkhitei(Newcomb, 1865).A recentreexaminationoftypes by Roth (1987a) showed D. whitneyi and D. cronkhitei to be conspecific. D. whitneyi has priority.
General Distribution--Discus whitneyi is distributed widely, occurring from Alaska and m u c h of Canada, southward into the northern half of the conterminous United States, and farther to the south along the mountains of the W e s t to southern Arizona and northwestern Chihuahua, México. In the Plains states, the species presently is k n o w n to live only as far south as South Dakota, but itsrange extended southward to Texas in the Pleistocene(Hubricht, 1985:Map 171).
N e w Mexico Distribution--Discus whitneyi occurs widely inNew Mexicomountains.ItistheonlyDiscusinthesouthern part of the state, whereas D. shimekii (see below) is a species of higherelevationsofthenorthernmountains.InNew Mexico,D. whitneyidoesnotdescendmuch below theTransitionLifeZone, although it descends lower in Arizona, even to the low, arid mountains ofOrgan Pipe National Monument (Dillon, 1980).
Discus shimekii (H. A. Pilsbry, 1890, as Zonites). The Nautilus, 4:3. T.L.: Iowa City, Iowa, as a Pleistocene fossil.(striatedisc)
Helicodiscus singleyanus (H. A. Pilsbry, 1889, as
Zonites).ProceedingsoftheAcademy ofNaturalSciences
of Philadelphia, 41:84. T.L.: N e w Braunfels, Comal Co.,
Texas.(smoothcoil) GeneralDistribution--Discusshimekiioccursinwestern
Seddon and Holyoak (1993:329) noted that Helicodiscus
scintillaLowe, 1852, isa seniorsynonym of H. singleyanus, and recommended that the case should be referred to the
International Commission on Zoological Nomenclature, with a view to preserving use of the n a m e singleyanus.
Helicodiscussingleyanusisoneofseveralsmallspeciesin the genus Helicodiscus that are confusingly similar to each other,itispossiblethatmorethanoneoccurinNew Mexico. Hubricht, who has studied this genus extensively, mapped (1985) three other members of the genus as living in Texas. Hubrichtalsomapped(Map 179)H.singleyanusasoccurring both living and fossil across Texas and into southeastern N e w Mexico, with other records to the east of Texas.
New Mexico Distribution and Habitat--Helicodiscus singleyanus has been taken at lower elevations in the southern
North America in Canada, and south to northern California, Arizona,andNew Mexico.LikeD,whitneyi,itoccurredasa Pleistocene species in the Great Plains region, but not sofar to the south as in the case of D. whitneyi.
New Mexico Distribution--Discus Shimekii occurs at
higherelevationsinthenorthernmountainsofNew Mexico,and asfarsouthastheSandiaandManzanoMountainsandMount
Taylor. AlthoughthespecieswasreportedbyPilsbry (1948:619)fromtheSanMateoandBlackRangeswestofthe Rio Grande Valley, in their original report on these ranges Pilsbry and Ferriss (1917:102) assigned disc shells only to Pyramidulacronkhitei(=Discuswhitneyi,above).We have found only D. whitneyi in these ranges. Discus shimekii is a species of the Canadian Life Zone and above, to treeline. In a t r a n s e c t o n t h e w e s t s i d e o f M o u n t T a y l o r , it w a s f o u n d a b o v e 10,000ft and in another transect, on the west wide of Lake Peak