Page 43 - Land Snails of New Mexico

18:4. T.L.: Big Hatchet Mountains, Hidalgo Co., N e w Mexico, with several "forms" listed and discussed in
Pilsbry(1946:129-134).
Dr. Edgar A. Mearns collected Holospiras in the Big Hatchet Mountains during his 1892 survey of the United States-México boundary. His party used a burro pack-train to ascend Hacheta Grande, highest peak in the range, from an easterly direction. In
1910, H. A. Pilsbry and L. E. Daniels spent a week in the Big
Hatchets,greatlyaugmentingthenumberofmuseum specimens
ofHolospirasfromthatrange.Pilsbrynoted(1946:128)that several thousand shells were collected.
Pilsbry (1915:334-344) devoted considerable study to the Holospiras that had been collected in the Big Hatchets by the above expeditions. He named several new forms in his publication, indicated above, and noted on p. 128 of his 1946 monograph that"TheHachetaholospirasbelong,ifwe accept the criterionof intergradation, to only one species, for which the prior name is H. crossei. Between this species and H.
bilamellata there is a perfect series of intergrades in size,
s c u l p t u r e a n d n u m b e r o f w h o r l s . . . ." H e n o t e d t h a t v a r i a t i o n
w a s great a m o n g populations in different parts of the range, but
that intergrades also were found involving these variants. Pilsbry
settled on recognizing two species, crossei and bilamellata. It
appears that these were the two extremes of the spectrum of
variation,discussedabove,sincehenoted(1946:128):"Forour
present purpose w e consider the smallest form (crossei) and the
largest (bilamellata) as species, ranking the others as
subspecies, though in some cases they are more distinct than
thesetwoarefromoneanother." ftinelevationandabout5,700ftatthesummit.Mostofthe
ItseemsclearthatPilsbryrealizedthathewas dealingwith morphological variants and not with discrete noninterbreeding s p e c i e s , o r e v e n w i t h g e o g r a p h i c a l l y i d e n t i f i a b l e s u b s p e c i e s . T h e assignment of names to such morphologically distinguishable forms may, of course, be useful in an informal context, but hardly advisable from a formal, biosystematic point of view. From thatstandpoint,itseemsbesttoassigntheBigHatchet Holospiras to the single species, H. crossei, which has line priority over H. bilamellata. In our collections from the Big Hatchets, we, too, have been impressed by the exhibited pattern of diversity, and, like Pilsbry, note that within populations there
are intermediates between smallest and largest specimens.
Distribution—Asindicatedabove,H.crosseiisanendemic
of the Big Hatchet Mountains complex. Its range extends
southward along a series of lower, linear, limestone hills to a smallisolatedmountainwestofthenorthernendoftheAlamo
Hueco Mountains. In 1985, living specimens were taken in limestone talus on the north-facing slope of this mountain ( N E 1/4, sec. 36, T32S, R16W).
Habitat--In higher reaches of the Big Hatchet Mountains, Holospiras are very common, where, as noted above, Pilsbry and Daniels collected several thousand specimens. This could be donetoday,aswell.DuringaNovember1988visit,wewere impressed by the large number of empty shells present along the northern cliffface of Hacheta Grande. Holospira crossei lives both on wooded slopes and in exposed locations. This latter tolerance is reflected in two of the subspecific names used by Pilsbry for Big Hatchet Holospiras: heliophila and insolita.
ridgeiscappedby amassive,marine-reeflimestoneoftheU Bar Formation of Lower Cretaceous age. Cliffs of this limestone c o m m o n l y r e a c h h e i g h t s o f 6 0 - 8 0 ft a l o n g t h e c r e s t o f t h e r i d g e . The habitat was discussed by Metcalf and Smartt (1974:58-59) as follows:
-
Snails were found mainly under large stones at the
b a s e o f t h e cliffs, e s p e c i a l l y i n a r e a s t h a t s u p p o r t e d
what seemed to be a slightly more mesic
vegetation. That is, in contrast to the sparsely
vegetated lower slopes of the ridge, the areas
directlybelow thecliffssupported a few small trees and shrubs:. ... A few mosses and ferns occurred
andgrassesandherbaceousplantsweremore
numerous in a narrow zone immediately below the
cliffs.The UBar Cliffsareperpendicular and reach
heights of 60-80 feet. The area along the
northeastern base of the cliffs is, consequently,
shadedformuch oftheafternoon.Possiblywater
fromsummerfreshetsspillsdown thebarerockto water the area below.
Populations of H. metcalfi were limited to the narrow, slightly m o r e m e s i c strip j u s t b e l o w t h e cliffs. L i v i n g s p e c i m e n s often occurred in aggregations of from three to ten individuals under and around the edges of large stones, and were taken at three localities.
Remarks--Holospira metcalfi, insofar as is known, is restricted to the very narrow area at the base of the U-Bar l i m e s t o n e cliffs, d i s c u s s e d a b o v e , a l o n g a f e w m i l e s o f H o w e l l s
HolospirametcalfiF.G.Thompson, 1974.Southwestern Naturalist, 19:53, Fig. 1. T.L.: Howells Ridge, Little Hatchet Mountains, Grant Co., New Mexico. (Metcalf holospira)
In his description (1974) of this species, T h o m p s o n stressed thatthespecieswas related closely to the Holospira complex of the Big Hatchet Mountains, which are located to the southeast of the Little Hatchets. In comparing the present species with Holospirabilamellata,(consideredasynonymofH.crosseiin theprecedingaccount,oftheBigHatchets,he noted:
They are similar in most aspects, but differ conspicuously in shape, the depth of the suture and the contour of the whorls. They are allopatric in distribution. The limestone outcrops occupied by the two species are interrupted by igneous intrusions and alluvial deposits which are ecologically intolerable to species of this subfamily. Because of the isolation of the two taxa from each other and because of the absence of
intergradingpopulations,Itreatthem asseparate
species though their interrelationship is close. Distribution and Habitat--Holospira metcalfi has a very limited range, being endemic to Howells Ridge at the northern end of the Little Hatchet Mountains. Since much of the Little
Hatchet range is of igneous bedrock, the habitat would be inimical to this calciphile elsewhere in the range. Howells Ridge isasoutheast-northwestlinearescarpment,about6mileslong and less than 1 mile wide. The base of the range is about 5,000
37