146 MANUAL OF NATURAL HISTORY. 



cal, simple, with an internal groove on middle 

 of right side ; operculum none. 

 9. Family. — Amphibolans (Amphibolidae). Ten- 

 tacles forming by their union a large frontal 

 disk with the eyes sessile on the fore part ; 

 shell spiral, turbinate ; outer lip notched in 

 the middle ; operculum horny. 



II. ORDER — Phaneropneumons (Phaneropneumona). 



Edge of mantle free from nape, leaving the pul- 

 monary cavity open ; operculum distinct ; animal 

 unisexual. 



I. SUB-ORDER. — Opisophthalmians (Opisophthalmata). 



Eyes sessile on upper part of head behind base of 

 tentacles. 



1. Family. — Looping-Snails (Truncatellidae). Eyes 



sessile behind base of tentacles ; tentacles 

 subulate ; foot divided across ; operculum 

 horny, sub-spiral ; shell turreted, spiral. 



II. SUB-ORDER. — Ectophthalmians (Ectophthalmata). 



Eyes placed on sides of head at outer base of 

 tentacles ; operculum horny or testaceous. 



2. Family. — Cyclostomes (Cyclophoridse). Eyes at 



outer base of tentacles ; foot moderate ; oper- 

 culum spiral ; shell with the aperture cir- 

 cular. 



3. Family. — Helicines (Helicinidse). Eyes at outer 



bases of tentacles ; foot elongate ; operculum 

 annular ; shell with the aperture semi-lunar. 



