152 



LAND AND FRESH-ATATEE SHELLS OF N. A. [PART IL 



Suborder THALASSOPHILA. 



Eyes sessile on the front part of the frontal disk formed by the 

 expanded tentacles. Operculum sometimes present. AniAal 

 marine, or living in the vicinity of the sea. 



There are two families now known to belong to this suborder, 

 one of which, Amphiholidse, is not represented in this country ; 

 species belonging to it are furnished with an operculum and are 

 still more marine in their habits than the Siphonariidse. Still, 

 they have the lingual dentition of Pulmouata, the mantle margin 

 nearly closed, and but rudiments of gills. 



Family SIPHONARIID.E. 



Lingual membrane broad, rather long; teeth numerous, 

 equal, in slightly arched, cross lines ; the central tooth nar- 

 row, elongated, with a small, rhombic apex ; the lateral teeth 

 larger, diverging, gradually diminishing in size towards the 

 outer side of the series, and furnished with a rather oblique, 

 curved tip. Head with a large frontal disk, bilobed in front, 

 and formed by the expanded tentacles ; eyes sessile on the 

 outer side of the disk. Eespiratory orifices covered by a 

 large fleshy lobe of the mantle. 



Operculum none. Shell conical, patelliform, with an in- 

 ternal groove on the right side. 



The Siphonariidss are marine in their habits, living near the 

 sea, on rocks between tide marks, or higher above the water but 

 dashed by the spray. 



The single genus of the family is represented in this country. 



SIPHOXARIA, Blainv. 



Shell trumpet-like_, orbicular, depressly conical ; apex sub- 

 central, oblique, recurved posteriorly ; aperture wide, margin 

 irregular„crenulated ; muscular impression crescentic ; a syphonal 

 groove on the right side, which is extended in a projection be- 

 yond the margin. 



