Introduction to Animal ]\IorpJiology. 3 1 1 



lariad3e — freshwater ; foot large ; eyes on short stalks ; pul- 

 monary cavity coexisting with the gills. 



§ V. Neurobranchiata — terrestrial, dioecious, operculige- 

 rous, breathing air by a vascular net-work on the roof of the 

 mantle cavity ; tentacles two, non-retractile, behind or at the 

 base of which are the eyes ; penis anterior. This includes : — 

 I. Cyclostomid:^ — shell conical, tcenioglossate, often de- 

 pressed ; foot long ; mouth round or oval, entire or with a 

 double margin ; operculum paucispiral or multispiral, horny 

 or calcareous. 2. Stoastomidse — shell conical ; columella 

 flattened ; eyes at the base of the tentacles ; radula rhipido- 

 glossal ; operculum not spiral, but semicircular, triangular, or 

 none. 3. Aciculidae — foot small ; lips parallel ; peritreme 

 thickened (Acicula), or canaliculated below (Geomelania). 



Order 2. Yxi\v[iOUZ.\.z. {Ciivier) — air breathing, symmetrical, 

 terrestrial, herbivorous, hermaphrodite Gasteropods, naked, 

 or shell-bearing, with no operculum, except in Amphibola. 

 The lung is behind the heart, and the larva has no con- 

 spicuous velum. The shell is deposited not outside, but as 

 calcareous granules, in the mantle substance. They are very 

 abundant in Avarm climates. They are divisible into three 

 sub-orders : — 



I. Acera — with no tentacles, including the Australian 

 family Amphibolidse, living in brackish water ; with the penis 

 under the right eye ; shell umbilicate, globular. 



Sub-order 2. Stylommatophora — eyes on the ends of 

 stalks or processes of the body wall (hinder tentacles), which 

 may be contractile and coexisting with two other simple ten- 

 tacles, as in Veronicella, or with no other tentacles, as in 

 Onchidium ; or the tentacles may be two ; retractile, as in 

 Janellidae ; or four retractile, as in the following families : — 

 Limacidae — shell hidden in the mantle (which is fused with 

 the back) ; jaws strong, crescentic. Arion has a shell of 

 several pieces and a caudal gland, as in Geomalacus, while 

 Limax, the common slug, has no tail gland. Parmacella has 

 a subspiral shell. 2. Testacellid^ — carnivorous, small; jaws 

 none ; the shell may include the whole body (Glandina), and 

 may have its last axis oblique (Streptaxis) ; it is rarely conical, 

 multispiral (Cylindrella), or small, as in Testacella and Dau- 



