272 DESCRIPTION OF A COLLECTION OF FOSSILS, 



thereby rendered subacute and undulated. Aperture long and narrow, widest in 

 the middle. Septum composed of numerous small lobes and saddles, apparently 

 about six lobes on the sides. The dorsal (or as it might perhaps more properly be 

 called, the abdominal lobe) is small, and lies entirely on the dorsal surface ; the 

 superior lateral lobe is much smaller than the second, from which the others 

 diminish regularly in size. The saddles are all comparatively simple except the first, 

 which is unequally divided. 



Measurements. Greatest diameter (apparently), about 3.5 in.; greatest width of 

 body whorl, about 1.75 in.; greatest width of aperture, 1.0 in. 



Locality/. "Immediate vicinity of Ollon, Prov. of Cajatambo; height 3000 

 metres. This rock appears to be Cretaceous." (R.) 



Remarks. Described from two fragments, one consisting of the body chamber 

 only, showing the broken remains of the first septum, a trace of the umbilical 

 margin, but a very good surface, although somewhat broken about the lower part 

 of the mouth. The species may be compared with A. placenta, DeKay, of the 

 Cretaceous of the United States, from the flat-backed variety of which it differs in 

 the dorsum being much wider, and bordered by tubercles instead of a smooth keel. 

 The ventral row of tubercles, of which traces remain in our specimen, is also 

 wanting in that species. From A. Pedernalis, Von Buch, which is sometimes 

 undulated on the sides, it also differs in all the above characters, and in the ventral 

 half of the sides not sloping down so gently to the umbilical margin. Prof. Hyatt 

 returned me the specimen figured, with the note following: "This I should con- 

 sider a variety oi BucUceras attenuatum, something between the form described by 

 me and that belonging to you (see figure of A. attenuatus, W. M. G.), see sutures. 

 It may be different, however, since I think I have seen Texas specimens like it, 

 and smooth throughout, A. H." I hardly feel warranted, however, in accepting 

 my friend's idea in this case, and venture to name the form. My reasons for 

 separating it are, from the (imperfect, it is true) view of the septum, obtainable 

 on the broken face, there seem to be fewer lobes than in Hyatt's species. This 

 specimen is nearly as large as the other, and it has developed in a markedly 

 different manner; the entire cross section of the whorl differs; there is no trace 

 of tubercles on the sides of the volutions, and the little tubercles on the umbilical 

 margin in this, are unrepresented in that. 



A. MACROCEPHALTJS, Schlot., PI. 39, fig. 1, la. 



Shell globose, sides and dorsum rounded; sides converging very slightly; 

 umbilicus minute ; whorls very deeply enveloped, the last almost entirely hiding 

 the preceding ; surface ornamented by small regular ribs, which arch forwards a 



