194 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



9. homalina, Stoliczka. 



Shell oval, subtrigonal, or more or less elongated, with anterior 

 side short and rounded, and posterior more produced and narrowly 

 rounded; fold nearly or quite obsolete ; hinge with one approximate 

 lateral tooth in the right valve. — T. alba, Linn. 



10. peron^ia, Poli (zz Omala, Schum., corrected Homala, by Agassi z ; 



also, Homala, H. and A. Adams). 

 Shell ovate ; anterior side shorter and rounded ; posterior sub- 

 acuminate ; hinge with lateral teeth obsolete. — T. planata, Linn. 



11. metis, II. and A. Adams. 



Shell oval or suborbicular ; posterior side shorter and subtrun- 

 cated; anterior rounded; hinder flexuosity sometimes submedian; 

 hinge without lateral teeth. — T. Meyeri, Phil. 



The foregoing is the arrangement of the sections of Tellina adopted by 

 H. and A. Adams, in their Genera of Recent Mollusca, excepting that I have 

 left out Arcopagia, and included an extinct group proposed by Dr. Stoliczka. 

 I have also adopted the name Homalina, of the latter author, instead of 

 Homala, H. and A. Adams, which latter name was pre-occupied by Agassiz's 

 correction of Omala, Schumacher, and is also synonymous with Peroncea, Poli. 

 Dr. Stoliczka also includes, as a section of Tellina, the group Arcopagia, 

 Leach, as well as Linearia and Tellinimera, Conrad. These types are 

 undoubtedly closely allied to Tellina; but it seems to me that the study of 

 this family of shells will be simplified by treating Arcopagia and Linearia as 

 distinct genera, rather than as sections of Tellina; the same may also 

 possibly be the case with Metis. Mr. Conrad's Tellinimera, as well as his 

 AZnona and CEne, were founded on shells presenting no external differences 

 from some of the sections of Tellina, and should possibly be ranged either 

 in or near that genus ; but as he has not yet illustrated or fully described 

 the hinges and interior of these types, I do not feel prepared to express an 

 opinion in regard to their rank and position. 



- As in many other cases, the question in regard to what particular species 

 should be considered the type of the genus Tellina is involved in some doubt. 

 Linnaeus, in 1758, defined it very briefly, and included a large number of 

 species, without saying or indicating which he considered the type. If we 

 take his first species as the type, a rule insisted upon by some, we would 



