400 MANUAL OF THE MOLLrSCA. 



Chondropoma (C. dentatum), is also said to occur in Florida, and Ampvllaria 

 depressa in Florida aud Georgia. 



18. American Region. 



The mass of American land and fresh-water shells are found in the central 

 and southern states, the country drained by the Mississippi and its tributaries. 

 The Heliclda are not more remarkable for size and colour than those of 

 northern Europe ; the most characteristic forms belong to the subgenus 

 Tohjgyra (or Tridopsis, Raf.), such as Helix tridentata, albolabris, hirsuta, 

 and sepiemvohns. The truly North American fcrms all belong to three 

 genera, viz. — Helix 43, Saccinea 8, Pupa 3 species. In the Southern States 

 are also found 5 sp. of Bulimus, 3 Cyliiidrellas, 2 Giandinas, and 5 Heliciose, 

 genera whose metropolis is in the Antilles or in tropical America. 



The fresh-water univalves include above 100 species of Melaniadce belong- 

 ing to the genera Ceriphasia, 31elafusus, Anculotas, Melatoma, aud Arnnlcola, 



15 Pahcdince, some keeled, and one muricated, {P. magnificn) \ and species of 

 Valvata, Limnaa, Physa, (15) Planorbis, and Ancylus, (5). 



The fresh -water bivalves are also extremely numerous ; the TJnionidije are 

 unequalled for their ponderous solidity, the rich tinting of their interiors, and 

 the variety of their external forms.* Gnathodon cuneatm, Cyrena floridana, 



16 sp. of Cyclas, and Pisid'mm alt lie, belong to this region. 



19. Oregon and California. 



The Fauna of the region beyond the Rocky Mountains is believed to be 

 almost entirely distinct from that of the United States. Arion (foliolatus) 

 and Llmax (Columbianus,) genera not indigenous to eastern America, 

 were found near Paget Sound, {Gould). We have no information respecting 

 the land and fresh-water shells of Russian America, but from analogy we 

 mav expect to find a few there identical with those already mentioned as 

 occurring in Siberia f 



The shells of Oregon and California are as yet only imperfectly known by 

 the researches of INIr. Nuttall and Mr. Couthouy. 



Helix 22 Pbysa 1 Cyrena 2 



Bulimus 1 Ancylus 2 Cyclas 1 



Achatina 1 Planorbis 3 Uuio 1 



Snccinea 4 Melania 2 Alasmodon 1 



Limnsea 4 Potamides 2 Anodon 3 



Limncea fragilis, a Canadian species, is said to range westward to the 

 Pacific ; and L. jugularis to be common to INIichigan, the North-west terri- 



* The private cabinet of Mr. Jay contains above 200 species of North American 

 Unionidce, and very many varieties. 



+ The affinity between the Mammalia of the Old and New Worlds is greatest in 

 eastern Asia and north-west America, and diminishes with distance from those regions. 

 — ' Waierhouse, in Johnston's Physical Atlas, No. 28.) 



