440 Systematic Paleoxtology 



the type of a distinct subgenus, for which I proposed the name Piesto- 

 chilus, in allusion to the closely appressed character of its outer lip above, 

 as compared with that of Clavellithes. At a still later date, in examining 

 other specimens, one of which was accidentally split longitudinally, the 

 discovery was quite unexpectedly made that it has one or two small, but 

 distinct, revolving plaits ascending all the way up the columella ; though 

 these are not seen at the aperture, especially when the latter is even partly 

 filled with foreign matter; while, if continued around, so as to be seen at 

 the inner side of the columella, they would appear at a higher position than 

 in the typical forms of Fasciolaria. This discovery led to the more critical 

 examination of the other Upper Missouri Cretaceous shells most nearly 

 agreeing in form and general appearance with the genus Fusus, when it 

 was found that these, too, possess one or more plaits, one, the columella, 

 not appearing at the aperture, but readily found by breaking open speci- 

 mens. Consequently, it becomes evident that probably none of our known 

 Upper Missouri Cretaceous fusiform shells can be properly retained in 

 the genus Fusus or Clavellithes, but that nearly all of them naturally 

 arrange themselves near, if not within, the genus Fasciolaria, thus con- 

 firming, as far as the evidence goes, an opinion expressed by the writer in 

 1864 in the Smithsonian Check List of North American Cretaceous Fos- 

 sils, that probably none of the species there provisionally retained in the 

 genus Fusus really belonged to that group. 



" A few species from older rocks have been referred to the genus Fascio- 

 laria; but we have good reasons for believing that this group, even as here 

 defined, was not introduced previous to the deposition of the later mem- 

 bers of the Cretaceous system. The number of species, especially of 

 typical Fasciolaria, was not even then quite limited ; but the species of the 

 Piestochilus and Crypiorhytis were more numerous. Indeed, it is highly 

 probable that a considerable portion of the Cretaceous shells that have been 

 referred by various authors to the genus Fusus, as well as some of those 

 referred to Fasciolaria, will be found to present the characters of one or 

 the other of the latter groups. I am not sure that either of these two latter 

 sections occur in the Tertiary rocks; but the typical section of Fasciolaria 

 ranges through the Tertiary, and probably attains its maximum develop- 



