76 PALEONTOLOGY OF NEW YORK. 



had before us for the study of this form, Mr. Billings' original specimens, which 

 give very clearlj- tlie interior characters of both valves. These were lucidly 

 described by the author, although he was not disposed to regard them as gener- 

 ically distinct from Obolella chromaUca. Tliis description, given upon page 70 of 

 the work cited, is in the following terms : 



'• Fi'om some nearly perfect casts of the interior, the following characters 

 can be made out. In one of the valves (supposed to be the ventral) a strong 

 rounded groove commences just beneath the beak, and runs along the median 

 line to about the center of the shell. On each side of the principal groove is 

 a large ovate nmscular impression, extending from near the mid-length of the 

 shell a little more than half-way to the beak. These impressions are bounded 

 and distinctly defined at their lower extremities by the two small, diverging 

 grooves above mentioned. Their outer and upper margins are distinctly de- 

 fined. In the rostral part of the shell there are two small grooves which take 

 their origin close to the beak, one on each side, and run toward the front, 

 diverging to the outside of the upper part of the two large muscular impres- 

 sions. The characters of the interior of the dorsal valve are somewhat similar 

 to those of the ventral valve, but the median groove is shorter, and there is a 

 thickening of the shell just below the beak, which presents the appearance of 

 a false area inside the cavity of the umbo. It is probable that the two small 

 grooves above mentioned are connected with the small muscular impressions, 

 which, in 0. chromaUca, are distinctly seen outside of the two larger. The 

 condition of our specimens, however, is such that this point must remain open 

 for fnrtlier investigation." 



In subsequently proposing to designate this shell by the term Billingsia (a 

 name afterwards changed to Elkania as the former proved to have been already 

 in use), Mr. Fouu gave a much enlarged and somewhat schematic figure of the 

 pedicle-valve (which we are disposed to believe emphasizes rather too strongly 

 the internal characters), and accompanies it with the following diagnosis of the 

 generic characters {loc cit., page 467) : 



" Shell thin, calcareous, inarticulate, longitudinally ovate or subcircular, con- 

 vex. Ventral valve with a solid beak and a minute area, which, in the typical 

 species, is grooved for the passage of the pedicle as in Obolella. Muscular 

 impressions in the ventral valve, six; one pair situated close to the cardinal 



