142 AMERICAN JOURNAL 



Genus RIMELLA, Agas. 



Spire elevated, whorls cancellated ; outer lip usually bordered 

 by an entire or denticulated, thickened margin ; anterior canal 

 short, straight or slightly curved ; posterior canal running up 

 the spire. 



R. crispata, R. fissurella, R. rimosa. 



Found as low as the newest Cretaceous. R. canalifera, nobis, 

 of the California Cretaceous cannot be separated from this 

 genus, and, so far as we are able to judge from the imperfect 

 material yet discovered, R. simplex, nob., is also a true Rimella. 



Genus ISOPLEURA, Meek. Plate 13, fig. 7. 



Shell subovate, spire moderately elevated, surface marked by 

 pretty even, large longitudinal ribs ; aperture narrow, notched 

 in front, outer lip simple, no posterior canal. 



I. curvilirata, Meek, = Rimella id., Con., 1. Meehiana, Gabb, 

 sp., Meek. Both Cretaceous. 



Genus CYCLOMOLOPS, Gabb., N. Gen. Plate 13, fig. 8. 



Spire elevated, whorls smooth, no anterior canal or notch, 

 posterior canal long, running up the spire ; columellar lip 

 covered with a thick callus, which, continuing around the ante- 

 rior end of the aperture, forms a thickened margin to the outer 

 lip. 



C. laevigata, = Rostellaria laevigata, Mellv. Eocene. 



Genus CALYPTRAPHORUS, Con. Plate 13, fig. 9, 10. 



Shell elongate, fusiform, spire high, anterior canal long and 

 straight ; posterior canal long, closely appressed to the spire 

 and arching on the back, as in some species of Hippochrenes ; 

 outer lip moderate, rounded and thickened on the margin by a 

 smooth border ; young shell showing all the volutions, which 

 are hidden in the adult by a polished incrustation covering the 

 entire surface, and in some species bearing tubercles or bosses, 

 their shape, size and number varying in different species. 



Calyptraphorus velatus, Con. 



Cretaceous and Eocene ; all of the species belonging to the 

 latter formation, except 0. palliatus, = Rost. id. Forbes, from 

 the Cretaceous of India. 



