Page 25 - Land Snails of New Mexico

do not affect overall appearance of the shell, which is glossy, even w h e n fossilized. In H. singleyanus, the umbilicus is shallower and wider, contained lessthan 3 times in width of the shell. In H. minuscula, the umbilicus is deeper and narrower, contained about 3 times or overin shell width. Inside view, the spire of H. singleyanus rises only slightly above the level of the top of the body whorl, whereas i n H . m i n u s c u l a , it r i s e s p e r c e p t i b l y m o r e t o f o r m a l o w d o m e .
Discidae
1a Shellstronglyribbedonbothupperandlowersurfaces....................................Discuswhitneyi(p.40)
1b Shellwithribsmoderatelydevelopedaboveandveryweaklydevelopedbelow .................Discusshimekii(p.40)
The differences between the above 2 species of Discus are subtle. Shells of D. shimekii seem glossier, probably because of less d e v e l o p m e n t o f r i b b i n g a n d m a n y s p e c i m e n s h a v e a n o l i v a c e o u s tint. P i l s b r y n o t e d ( 1 9 4 8 : 6 0 3 , 6 1 8 ) t h a t i n D . w h i t n e y i , u m b i l i c a l w i d t h is c o n t a i n e d f r o m 2 . 4 t o 2 . 8 t i m e s i n s h e l l w i d t h , a n d i n D . s h i m e k i i , 3 . 7 t o 4 t i m e s . E v e n w i t h c a s u a l i n s p e c t i o n , t h e u m b i l i c u s a p p e a r s wider in D. whitneyi. In D, whitneyi, also, the body whorl is less capacious, more angular, and the sutures more deeply impressed than inD.shimekii.DiscusshimekiioccursinhighermountainsinnorthernNewMexico(southtoMountTaylorandtheManzano Mountains), while D. whitneyi occurs over a broad elevation range in mountains throughout the state.
Succineidae
ShellsofOxylomaretusumcanbedistinguishedfromthoseofotherspeciesbytheirgreaterheight,of12mm ormore,andthehigh, narrowaperture,whichreachesca.70%ofshellheight.Inotherspeciesofsuccineidsinthestate,shellheightis<12mm andapertural height only 50-60% of shell height. Shell characters are inadequate to determine species in the genera Succinea and Catinella, and charactersofthegenitaliahavebeenusedinsteadinmakingspeciesdeterminationsinthesegenera.Wu (1993)hasillustratedsomeof thesecharactersforspeciesofNew Mexico ................................................................ (p.47)
la
lb
2a
2b
3a
3b
4a
4b
5a
5b
Zonitidae
Matureshell4.5mmormoreinwidth,freshshellsglossy....................................................2
Matureshell<3.5mminwidth,freshshellsnotveryglossybecauseofnumerousgrowthlinesorribs.................5
Matureshell>10mm indiameter,inurbanareas ...................................Oxychilusdraparnaudi(p.65)
Matureshell<7mmindiameter,mainlyinnon-urbanareas...................................................3
Freshshellglossyandwithbrownishperiostracum;withoutincisedgrooves................Zonitoidesarboreus(p.51)
Freshshellveryglossywithcleartowhitish(neverbrownish)periostracum.ThesearetheonlyNewMexico
land snails to have well-defined incised grooves (indented below the shell surface). Grooves are parallel
to the growth lines .................................................................................... 4
Shellperforate(i.e.,umbilicusreducedtoaslitasitismainlycoveredoverbythecolumellarwallofthe
body whorl); aperture lunate (i.e.,wider than high) .................................. Glyphyalinia indentata (p. 50)
Shellumbilicate(i.e.,umbilicuswell-developedandobservable);aperturerounded(aboutaswideashigh) ******************************************************************** Nesovitreahammoniselectrina(p.50)
Shellwithnumerous,closelysetriblets,umbilicusshallow,flatandwide,bodywhorlslightlyexpanded. Shellmottledwithvariouscolors:white,gray,andbrownhues,severaladjoiningribsmay bewhite
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Striaturameridionalis(p.51)
Shellwithoutriblets,butwithclose-setgrowthlines(likewovensilkthreads);umbilicusnarrowand
deep, shell light tan, not mottled, body whorl not expanded. Further information is provided under Helicodiscussingleyanus,above ...................................................Hawaiiaminuscula(p.50)
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