126 MANUAL OF NATURAL HISTORY. 



to discover, securely lodged, the curious Magilus and 

 the Leptoconchus. 



III. Class.— GASTEROPODS (Gastero- 

 poda). 



Head distinct, furnished with eyes and tentacles ; 

 body usually protected by a spiral or conical shell ; 

 adult walking on an expanded foot. 



I. SUB-CLASS. — Prosobranchs (Prosobrauchiata). 



Heart placed behind gills ; sexes distinct ; gills 

 comb-like, on back of mantle or round its edge. 



I. ORDER. — Pectinibranchs (Pectinibranchiata). 

 Gills formed of one or two series of laminae on left 

 side of mantle over back of neck ; shell spiral. 



I. S UB-ORDER. — Proboscidiferous-Pectinibranchs 

 (Proboscidifera). 



Head with a long retractile proboscis ; tentacles 

 close together at their origin ; eyes sessile at their 

 outer bases. Carnivorous. 



1 . Family, — Rock-Shells (Muricidae). Teeth in three 



rows ; mantle with a long straight siphon ; 

 foot simple in front ; shell with a more or 

 less elongated canal at fore part of aperture ; 

 whorls with varices. 



2. Family. — Trumpet-Shells (Tritonidse). Teeth in 



seven rows ; mantle enclosed, with a straight 

 siphon ; shell with irregular or few varices 

 on the whorls; aperture with an elongated 

 siphonal canal. 



3. Family. — Whelks (Buccinidse). Mantle enclosed ; 



