- l.:^7 - 



tinguished by its more prod'aoed posterior margin, the varying char- 

 acter of the ribs in different -portions of the shell, thinner shell, 

 and finer^ shorter and more numerous teeth, jlnother species from 

 the same horizons, A. ( Sjapharoa ) hr.-ooniela Dall fl) is readily dis- 

 tinguished when adult since the ^loridian foim is much larger, more 



(1). loc. eit., p. 657, pi. ?5, fi^-. 1, 1898; Bull. IT. S. Fat. 



Muc, no. 90, p. 121, pi. 17, fi?. 7, -ol. 21, figs. 17, 18, 1915 



inflate", tn.incated posteriorly rather than acutely rotuided and the 

 ribs, except those on the posterior slope are deeply channele:"; 

 young individuals of the same size as inaeguilateralis are similar 

 In a-opearance, es^cially those from the silex he's, because of 

 their thin shells, but they always have sulcate'l ribs and are not 

 quite as much rirodiice i and rou-~.ded posteriorly. A, gatunensis 

 Toula (S), described fit) m Oatim, Panan;a is larger, '• : -ier, more 



(2). Jahrb. E. S. Geol. Reichsanstalt , vol. 61, p. 4-91^, ^dI. 50, 

 fig. 4, 1911. 



convo", less produce''"' posteriorly, the anterior ribs are more deep- 

 ly sulcate, the me'lian ribs narrower and sharper and the ribs ir.ined- 

 iately anterior to the posterior slope are sulcated. Brov/'n and 

 Pilsbry have described another more closely related Gatun form - 



