GASTEEOrODA. 285 



lines. South Seas (= Echinospira, Krolin and Jasonilla- 

 Maed). 



Becluzia, Petit, 1853. R. Jehennei, Eed Sea. E. Eollandiana, 

 Atlantic, and Mazatlan. 



Animal pelagic, resembling iantMna ; one inch. long. 



Shell paludiniform, thin, with a brown epidermis ; whorls 

 ventricose ; aperture orate-oblique, slightly effused at the base, 

 margins disunited ; inner lip oblique, rather sinuated in the 

 middle ; outer lip acute, entire. 



These so-called genera, formerly thought to belong to the 

 Atlantidse, are, for the most part, composed of prosobranchiate 

 laryse ; but the genera to which they belong has not yet been 

 ascertained. 



OEDER II.— PULMONIFEEA. 



This order embraces all the land- snails and other mollusca 

 which breathe air. They are normal gasteropods, having a 

 broad foot, and usually a large spiral shell ; their breathing- 

 organ is the simplest form of lung, and is like the branchial 

 chamber of the sea- snails, but lined with a network of 

 respiratory vessels. One large division of the land-snails is 

 furnished With an operculated shell ; the rest are in-operculate, 

 and sometimes shell-less. 



The pulmon'ifera are closely related to the plant-eating sea- 

 snails (holostomoia), through Cydostoma, and to the nudibranchs 

 by Oncidium. As a group, they are generally inferior to the 

 sea-snails, on account of the comparative imperfection of their 

 senses, and the union of the functions of both sexes in each 

 individual. 



Section A. — In-operculata. 



The typical pulmonifera vary much in appearance and habits, 

 but agree essentially in structure. Most of them have suffi- 

 ciently large shells ; in the slugs, however, the shell is small 

 and concealed, or rarely quite wanting. Snail- shells contain a 

 larger proportion of animal matter than sea-shells, and their 

 structure is less distinctly stratified (p. 32), In form these 

 shells represent many marine genera. The greater part are 

 terrestrial, only some of the smaller families inhabit fresh 

 waters or damp places near the sea. The respiratory orifice is 

 small and valve-like,* to prevent too rapid desiccation in the 

 land-snails, and to guard against the entry of water in the 

 « Hence tliey ai-e called Adelo-pneumona (concealed-lunged) by Gray. 



