<684 ZOOLOGY SECT. 



Salt-Order 1. Platypodn. 



Pectinibranchia with the foot flattened ventrally, at least in 

 front. Jaws are nearly always present. 



This sub-order includes the Cowries, the Vermetes, the Tritons, " 

 the Whelks, the Cones, and a number of other groups. 



Sub-Order 2 . He teropoda . 



Pelagic Pectinibranchia with the foot laterally compressed and 

 bearing, at least in the male, a ventral sucker. The visceral sac 

 and mantle form only a small part of the mass of the body. Jaws 

 are absent. 



Sub-Class II. Euthyneura. 



Gastropoda in which the visceral commissures are not twisted 

 into a figure of 8, and in which the sexes are united. 



ORDER 1. OPISTHOBRAXCHIA. 



Marine Euthyneura with aquatic respiration, the auricle of the 

 heart usually posterior to the ventricle. The mantle-cavity, when 

 present, opens by a wide aperture. 



Sub-Order 1. Tcctibntin-// in. 



Opisthobranchs provided in nearly all cases with a mantle and 

 a shell, nearly always with a true ctenidium, and an osphradium. 



This section includes the Ajylysiidcc, or Sea-hares, and several 

 other families, including certain pelagic Gastropoda, some shell- 

 bearing, some shell-less, formerly regarded as constituting a 

 distinct class the Pttropodn. 



Sub- Order 2 . Nudibi -a nc/t ia. 



Opisthobranchs, which are devoid of shell in the adult condition, 

 and have no true ctenidia or osphradium, respiration being carried 

 on by means of secondary branchise usually arranged in a circlet 

 around the anus or in rows on the dorsal surface, or laterally under 

 the edge of the mantle. 



This sub-order includes Doris, Eolis, Tetliys, and other shell-less 

 forms. 



ORDER 2. PULMONATA. 



Euthyneura devoid of ctenidia, respiration being carried on 

 through the Avails of the mantle-cavity, which has a narrow 

 contractile aperture. 



This sub-order includes the Land Snails and Slugs. 



