480 Recent freshwater 3Iolliisca, 



are enumerated, (or 33, including Mexico,) of which no less 

 than eight occur in Europe ; and, of these eight, common 

 to Europe and North America, but one has been detected in 

 the West Indies. Erichson cites three species of Brachelytra, 

 common to Europe, Asia, and America ; another, as common 

 to these countries and South Africa ; three, as found in Europe 

 and South America ; and but a single species as appertaining 

 to both divisions of the American continent.* The last fact 

 is a curious one, and shows how very distinct the faunas of 

 approximate regions may be. The author, to whom I have 

 just alluded, remarks that northern species may be found in 

 the mountains of temperate regions,! and cites Tachinus 

 elongatus as occurring in Sweden, Unalashka, and the moun- 

 tains of Switzerland. 



Mr. Westwood states that a large species of Cybister (an 

 aquatic coleopter) occurs at Senegal, Guinea, Cape Good 

 Hope, Madagascar, Mauritius, and in the Indian archipelago ; 

 and Mr. Kirby, that Sphodrus terricola inhabits Great Britain 

 and Valparaiso,! Carabus vietinghovii, Siberia and America, 

 and a species of Isopleurus, India and the Rocky Mountains. <§> 

 M. Laporte affirms || that Nogrus griseus is found in the four 

 quarters of the globe ; and M. Guerin IVIenevilie, that a crus- 

 tacean, (Pontonia custos) found parasitic in bivalve shells at 

 Rio Janeiro, is identical with individuals from the Morea. 

 Probably Libiniacana, liculata Say, and certainly Cancer irro- 

 ratus. Say, inhabit the Atlantic and Pacific coasts of North 

 America ; H and, according to Professor Ehrenberg,** two 

 thirds of the microscopic protozoa hitherto detected on our 

 continent, inhabit Europe also. 



Of the species indicated in the list at the head of this 

 paper, Paludina vivipara is found in Ireland, England, Swe- 

 den, Germany, and Sicily ; Physa hypnorum in the same, 



N 



* North and South America present us with entirely distinct groups of many- 

 animals, as in the order Rodent ia. 



t See Dr. Pickering's botanical map, in the Amer. Phil. Trans., vol. iv. 



t Bridgw. Tr., Am. ed., p. 29. § lb. p. 494, note. 



II Ann. Ent. Soc. Fr. i. 397. IT Journ. Acad. N. S. viii. 106, 116. 



* * Am. Journ. Sci. xlvi. 309. 



