xxii. GOI^GEYLIA—DITHYRA. 



3. plicata, lamelloso-plicata, anticd dilatata. 



with laminar plaits, dilated at the anterior end. 



5. HiATELLA. 



1.' minuta, posticS truncata ureolata. 



truncate with an impression at the hinder end. 



2. oblonga, postici rotundata, areola nulla. 



rounded at the hinder end, without impression. 



6. Pethicola. 

 1. Irus, Petricola. 



7. Venerupis. 



J . perforans, Venerupis. 



8. Mya. 



1. truncata, anticS truncata, dente mutico. 



truncate at the anterior end, with the tooth 

 simple. 



3. ovalis, antici rotundata, dente flexuoso. 



rounded at the anterior end, with the tooth 

 flexuous. 



2. arenaria, antice rotundata, dente denticulate, 



rounded at the anterior end, with a denticle on 

 the tooth. 



9. Lyonsia. 

 1. striata, Lyonsia. 



