Page 16 - Land Snails of New Mexico

10
Figure3.ShellformsandshapesofNewMexicolandsnails.A,Pupilliform(Pupillamuscorum,3.1mm high),B,urocoptiform(Holospiracrossei, 13.6mm high),C,bulimoid(Rabdotusdurangoanus,15.6mm high),D,succiniform(Succineagrosvenori,12.4mm high),E,decollate(Rumina decollata14.0mm high),F,fusiform(Cionellalubrica,6.5mm high),G,cylindrical(Columellacolumellaalticola,2.7mm high),H,ovate-conic (generalizedVertigoshellnotshowingteeth),I,elongate-conic(Pupoidesalbilabris,4.8mm high),J.dome-shaped(Euconulusfulvus,3.2mm wide), K,depressedshell(Sonorellaorientis,17mm wide),L,subgloboseshell(Humboldtianaultima,13.5mm wide),M,angularshell(Ashmunella organensis,14.6mm wide),N,keeledshell(Oreohelixmetcalfei,14.8mm wide),O,discoidshellshowingraisedlirae(Helicodiscuseigenmanni,
4.5mm wide),P,shellshowingribs(Valloniagracilicosta,2.7mm wide).
than the adjoining part of the body whorl (Fig. 2A, right). However, with thickening of the peristome, the parietal wall b e c o m e s m o r e a s t r u c t u r e i n its o w n r i g h t ( F i g s . 2 A , left, F - H ) , and in extreme cases (e.g.,Metastoma roemeri) itmay be entirely separated from the body whorl behind it. From the outermostcorneroftheparietalwall,theentirelyfreeouterlip starts its descent, continues downward, and then curves back towards the columellar wall. The upper part of the outer lip, which is predominantly vertical in orientation is called the
• -
palatal wall. The bottom part, which isbasically horizontal in orientation, is called the basal wall. Distinction between the palatal a n d basal walls m a y b e rather arbitrary.
Thethickened(calloused)peristomewallsofshellsmaybear various kinds of small projections. A practical, all-inclusive namefortheseisteeth,whichwe shallusehere.However,some authors call them denticles (little teeth), while others use the more complex term apertural barriers. Pilsbry (1948:869) noted that teeth found on the columellar wall should, properly,
angularity
|
lirae O
keel