45 '3 Trans. Acad. Sci. of St. Lows. 



revolving costae about ten in number, the first two or three 

 above the peripheral band being finer than the others, these 

 two sets of markings give to the upper surface of the volu- 

 tions a reticulate ornamentation ; the peripheral band marked 

 by transverse costae concave outward, about equal in size or 

 a little coarser than the transverse costae above the band and 

 as about twice as numerous, giving to the band a crenulate 

 appearance ; below the peripheral band the surface is marked 

 by numerous fine, revolving costae and by fine transverse 

 costae, both sets of markings being much finer than those 

 upon the upper surface of the volutions. 



The dimensions of a nearly perfect specimen of average 

 size are: height, 6 mm.; maximum diameter, 6 mm.; 

 height of aperture, 3.3 mm. ; width of aperture, 3.3 mm. 

 largest specimen observed, an imperfect one, has a maximum 

 diameter of 8 mm. 



Bellerophon ulrichi n. sp. 



Plate 2, Jigs. 20-23. 



Description. Shell of medium size, umbilicate, with about 

 three volutions in the adult; outer volution ventricose, in- 

 creasing in size regularly to near the aperture where it is 

 more or less abruptly expanded, cross-section of the volutions 

 subelliptical. Aperture subelliptical, the outer lip thin and 

 sometimes somewhat produced with a shallow dorsal notch 

 one millemeter or less in depth, the inner lip extended over 

 the volution and much thickened laterally around the umbili- 

 cus. Surface marked with a dorsal band extending from the 

 shallow dorsal slit, which is usually somewhat smoother than 

 the lateral surfaces, it is even with the general surface of the 

 shell or sometimes slightly depressed, until it approaches the 

 aperture when it is gradually elevated, becoming conspicu- 

 ously elevated upon the abruptly expanding portion of the 

 shell at the aperture. The lateral surfaces of the shell marked 

 with fine, more or less regular, transverse lines of growth 

 which are often inconspicuous except towards the aperture 

 where they become more irregular and more or less crowded, 

 as they approach the dorsal band they bend backwards around 

 the dorsal notch. 



