Page 17 - Land Snails of New Mexico

be called folds, and those of the parietal wall should be called lamellae. But, Pilsbry frequently resorted to use of the word "tooth," as well.
Folds and lamellae (terms that w e mainly avoid here) are elongateoutgrowthsofthewallthatextendvaryingdistances backintotheshell.Casuallylookingattheaperture,oneusually sees only the front end of such a longer structure, so that they also look tooth-like. Lamellae extending back along the palatal or basal wall can be discerned in some cases on the outside of the shell if the wall is sufficiently thin. Some teeth may be located so far back from the aperture that they are not visible at all in apertural view.
Usually, teeth can be allocated as being on one of the subdivisions of the peristomial wall discussed above. Thus, w e may have columellar,parietal, palatal, or basal teeth (Fig. 2F). A secondtooth,locatedtotheoutersideoftheparietaltoothon the parietal wall is given a special name: angular tooth (Fig. 2G). In some snails, the parietal and angular may be combined into a single angulo-parietal tooth (Fig. 2H). Except for the case of the angular, additional teeth are named by adding the adjectives upper and lower and the prefixes supra, infra, sub, or inter. For example, there may be a supracolumellar or subcolumellar tooth or an upper or lower palatal tooth, with an interpalatal tooth between them (Fig. 2H).
We haveavoidedusingthetermsrightandleftindiscussing shell orientation. However, these terms are used to indicate differences in the direction of coiling in snails. Actually, all species of N e w Mexico land snails typically exhibit what is called right-handed or dextral coiling. In a shell with this type of coiling the outer free lip (palatal wall) of the aperture is located to the viewer's right. In left-handed or sinistral coiling, this lip is l o c a t e d t o t h e left. O n e c o m m o n g e n u s o f N e w M e x i c o a q u a t i c snails(Physa)exhibitssinistralcoiling.We havefoundafew atypical, sinistral specimens of land snails, mainly in the genus Pupilla. In the snail Metastoma roemeri, the last whorl is twisted in such a w a y as to give a false impression of sinistral coiling.
In the key for families, below, several terms are used (as in Burch, 1962) that refer to a distinctive shell form that is typical ofaparticularfamily.The followingformsareillustratedinFig. 3A-D, and include pupilliform (for Pupillidae), urocoptiform (forUrocoptidae), bulimoid (for Bulimulidae), and succiniform (for Succineidae). Other, more general terms referring to shell shape (Fig. 3E-J) are also employed such as decollate, fusiform, cylindrical,ovate-conic,elongate-conic,anddome-shaped(this last term in reference to the spire). In discoid shells (Fig. 3O), thebodywhorlisflattenedasseeninaperturalview.From such discoid shells, there is a gradation in degree of elevation of the shell from depressed (Fig. 3K) to globose. Globose shells are almost spherical. N o N e w Mexico land-snail shells reach the extreme of being globose, although several are elevated to the degree indicated in Figure 3 L as subglobose. T h e periphery of the body whorl (as seen in apertural view) may be rounded, angular or carinate (Fig. 3K-N). Carinate shells have a prominent spiral ridge-like cord or keel, which surrounds the shellatthepointofmaximum angularity(Fig.3N).
The surface of shells may bear various kinds of distinguishing features. Pigmentation of the periostracum gives
rise to color patterns that are usually whitish, grayish, or brownish in our species. Some of these pigmentation patterns are useful in identification. Raised or depressed features of the shell surface are referred to as sculpture or, occasionally, as ornamentation.Themostcommon sculpturalfeaturesconsistof growthlines(Fig.3A).More stronglydevelopedridges,which are oriented like, and often originate as, growth lines are termed ribs(Fig.3P).RibsarefoundinnumerouskindsofNew Mexico land snails. In their orientation, ribs m a y range from oblique to vertical. Raised lines that are parallel to the plane of coiling or of the sutures, i.e., are spirally oriented, are called lirae (Fig. 3O). O u r only species that clearly exhibit lirae are Helicodiscus eigenmanni, Oreohelix barbata, and Oreohelix pilsbryi, although high magnification may reveal faint lirae in other species. All the above sculptural types are raised features. In contrast, there m a y be incised, shallow grooves on the surface of the shell. Incised spiral grooves are called striae. However, in our species, such minute grooves are parallel to the growth lines, and are well developed only in the genera Glyphyalinia and Nesovitrea in the family Zonitidae (Fig. 2B-C).
USE OF KEYS FOR LAND SNAILS OFNEWMEXICO
The identifying of New Mexico land snails could be approached in several ways. The use of shell characters is a traditional approach, and the one mainly employed here. In some guides to southwestern plants, altitudinal Zonation has been employed in characterizing plant communities and as an aid in identifyingspecies.Such an approach willbe incorporatedhere, insome instances,usingtheLifeZone scheme, discussed earlier. Another approach that is useful in categorizing and identifying New Mexico land snails is provided by their patterns of distribution. In m a n y instances a species is restricted to (=is endemicto)aparticularmountainrangeorgroup ofranges.This is especially applicable to larger species inhabiting the southern halfofthestate,where such endemism ismarked. For example, asnailofthegenusSonorella,knowntocomefromtheDoña A n a Mountains will almost surely prove to b e Sonorella todseni. Various combinations of the above approaches will be employed, herein, wherever they seem useful.
A keytothefamiliesoflandsnailsfoundinNew Mexicois provided below. In cases where the family comprises more than one species, an additional key for that family is provided after the generalkeytofamilies--"AKey toGeneraandSpecies."Inmost cases these individual keys for families take identification to the level of species or subspecies. In cases where only one N e w Mexicogenusorspeciesoccursinafamily,thenameofthe species is indicated in " A K e y to Families." In the key, at s o m e points, explanatory comments are interposed between statements. Itishoped that most of the terms encountered will have been covered in the foregoing discussion and in illustrations in Figures 2 and 3.
In the dichotomous keys, one simply commences with number 1, chooses 1a or lb, and then proceeds as directed, either to another number or to a taxon name, which may be
family, genus, species, or subspecies, depending on the key that is used.
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