<>84 ZOOLOGY SECT. 



'Sub-Order 1. Platypoda. 



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. Hcteropoda. 



Pelagic Pectinibranchia with the foot laterally compr 

 bearing, at least in the male, a ventral sucker. The visce^ 

 and mantle form only a small part of the mass of the body, 

 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. OPISTHOBRANCHIA. 



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 . Tectibranchia. 



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 Jiplysiidce, 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 Pteropodn. 



Sul>- Order 2 . Nudibrancliia . 



Opisthobranchs, which ^ire devoid of shell in the adult condition, 

 and have no true ctenidia or osphradium, respiration being carried 

 011 by means of secondary branchiae 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, Tethys, and other shell-less 

 forms. 



ORDER 2. PULMONATA. 



Euthyneura devoid of ctenidia, respiration being carried on 

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

 contractile aperture. 



This sub-order includes the Land Snails and Slugs. 



