INVERTEBRATE PALEONTOLOGY. 357 



of a distinct subgenus, for which I proposed the name Piestochilus, in allusion 

 to the closely-appressed character of its outer lip above, as compared with 

 thai of Clavettithes. At a still later date, in examining other specimens, one 

 of which was accidentally split longitudinally^ the discovery was quite unex- 

 pectedly 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 Mis- 

 souri 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 on the columella not appearing at the aperture, but readily found by 

 breaking open specimens. Consequently, it becomes evident that probably 

 none of our known Upper Missouri Cretaceous fusiform shells can be properly 

 retained in the genus Fust/* or Clavellithes, but that nearly all of them 

 naturally arrange themselves near, if not within, the genus Fasciolaria; thus 

 confirming, 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 belong to that group. 



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

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

 defined, was not introduced previous to the deposition of the later members 

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

 Fasciolaria, was even then quite limited; but the species of the Piestochilus 

 and Gryptorhytis 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 development in our existing seas, 

 where some of the species grow to great sizes. 



The section Terebrispira was founded on a Miocene species, and will 



