498 MOLLUSCA 



SUB-KINGDOM VI 



Punctinae. Jaw of numerous separate plates ; shell minute. Includes the 

 Holarctic genera Punctum, Morse, and Sphyradium, Charp., and the New Zealand 

 genus Laoma, Gray. Recent. 



Endodontinae. Jaw-plates united more or less completely. Genera : Pyramidula, 

 Fitz. Discoidal or low conic, with tubular ribbed whorls and open umbilicus. Car- 

 boniferous to Recent. This is one of the most ancient land Mollusks known, and is 

 the oldest Helicoid form. Phasis, Amphidoxa, Flammulina, and Endodonta, Alb., are 

 similar austral forms, but are only known Recent, 



Family 4. Arionidae. 



Slugs having the shell reduced to a flat plate or a few granules, nearly or entirely 

 concealed, or absent. Mantle in the form of a shield on anterior part of the body ; teeth 

 of the quadrate type. Recent. 



This family is probably derived from the Endodontidae by degeneration of the 

 shell. Arion, Fer., and Anadenus, Heyn., are leading genera of Europe and Asia ; 

 Ariolimax, Morch., and Prophysaon, Bland, those of North America. 



Family 5. Philomycidae. 



Slugs somewhat similar to Arionidae, but the mantle covers the entire upper surface 

 of the body. A shell is completely absent ; hence no fossil forms are known. 



Superfamily 4. ELASMOGNATHA. MSrch. 



,A Jaw with a strong squarish process of attachment above. 



\j^ Family 1. Succineidae. 



FIG. 1048. Shell thin, ovate, consisting of few whorls. 



SanS^Low^S: Succinea, Pfeiffer (Fig. 1048). Shell thin, ovate, amber-coloured, 

 cene ; Tuchoritz, translucent, with short spire, and large body whorl. Outer margin 

 of aperture sharp. Tertiary and Recent ; abundant in the Loess. 



Range and Distribution of the Gastropoda. 



Of all classes of Mollusks, the Gastropods exhibit the most manifold 

 variety. Beginning in the Cambrian, they acquire a very gradual increase 

 and distribution, and are at present enjoying their maximum vigour. There 

 exist probably over 20,000 recent species, about three-fifths of which have 

 gills, the remainder being air-breathers. 



At the base of the Cambrian (Olenellus zone) are found such archaic 

 genera as Scenella, Stenotheca, Platyceras, Rhaphistoma, Pleurotomaria, and a 

 number of doubtful Pteropod-like forms (Hyolithes, Hijolithellus, Salterella, Torel- 

 lella, etc.), which evince the great antiquity of the Aspidobranchs and forms 

 resembling the Capulidae. In the later Cambrian the Ehipidoglossa (represented 

 by the Pleurotomariidae, Euomphalidae, and Bdlerophontidae) predominate ; and 

 associated with these are certain Pteropod remains, members of the Capulidae, 

 and a few genera probably referable to the Turbinidae. A notable genus 

 occurring here is Subulites, which bears some resemblance to the Pyramidellidae, 

 and exhibits a distinct channelling at the base of the columella." 



Unfortunately the poorly preserved remains of Cambrian Gastropods afford 



