

464 CHAMETRACHiEIDiE. 



pellis-phocae, Reeve. ruderalis, Lam. 



pellucida, Brod. Riippellii, Reeve. 



prsetexta, Reeve. sarda, Reeve. 



producta, Brod. sordida, Brod. 



radians, Lam. variegata, Reeve. 

 rubea, Reeve. 



Sub-gen. arcinella, Schumacher. 



Shell spinose, nearly regular and equivalve, always attached 

 by the right umbo; lunule distinct. 



echinata, Brod. spinosa, Schum. 



Fam. CHAMETRACILEIILE. 



Animal free, or attached by a byssus. Mouth oval, with 

 large, narrow lips, at the end of which are the narrow, 

 pointed, labial palps. Mantle double-edged, the inner edge 

 expanded; pedal opening small, anterior, under the beaks ; 

 siphonal orifices surrounded by a thickened border, the 

 branchial plain, the anal remote, with a tubular valve ; 

 gills two on each side, narrow, plicate, united behind, the 

 outer pair composed of a single lamina, the inner thick, 

 with grooved margins. Foot small, thick, cylindrical, with 

 a byssal groove. 



Shell regular, equivalve, truncate anteriorly; surface of 

 valves strongly ribbed ; margins dentate. Ligament exter- 

 nal. Muscular impressions united, the hinder large, sub- 

 central, the anterior obsolete. 



Genus CHAMETRACH.EA, Klein. 



Shell regular, equivalve, transverse, triangular, inequi- 

 lateral, solid, with a large byssal sinus in each valve in 



