NATTILTD^. 
107 
that group in having a perforated nmbilicns^ ; while the whorls are 
less compressed, narrower [7 e. laterall}^], and provided with several 
distinct revolving angles and grooves. They also differ in being 
often ornamented with well-defined revolving lines. In the per- 
forated character of the umbilicus the shells of this group may not 
differ from some other sections of discoid fossil Xautili^ but in the 
possession of several distinct revolving grooves and angles, with 
strong longitudinal striae, they seem to be quite peculiar. The 
group appears to be mainly, if not almost exclusively, confined to 
the Carboniferous System, and will include the following foreign 
species : — Xautihis sti/r/ialis, X. Edtuarclsianus, X. Omalianus, and 
X pin^ius^ de Koninck [not X. pin^uis^ M‘Coy], together with 
X. sulcatus, X. ccrriniferus, &c. of [J. de C.] Sowerb)'". 
“ After proposing the foregoing name [^Trematodisciis'] and descrip- 
tion for this ancient group of Xautili, we observed that Prof. 
M‘Coy had proposed, in his ‘ Carboniferous Fossils of Ireland,’ 
p. 20, 1844, the name Temnocheilus for a group of Carboniferous 
species, including some of the same species for which our name 
Trematodiscus was proposed. As his subgenus, however, embraced 
a much wider diversity of forms than ours, it may be found con- 
venient to restrict it to such types as his first species X. hiangidatus, 
X. pinffuis (M‘Coy, not de Kon.), and X. glohatus . . .” These 
species are now, however, included in the present genus. 
The name Vestinautilus, which is here treated as a synonym, 
was proposed by Pyckholt in the pamphlet already cited, and which 
appears to have had a very limited circulation. Vestinautilus is 
referred to by de Koninck in his able review of the literature of the 
Xaufilidce^. After describing the features in Kyckholt’s fossils, 
upon which that author based his genus, de Koninck points out that 
the latter cannot be recognized, as it was evidently founded upon 
an error of observation, Piyckholt believing that he recognized in 
one of the layers of the test a character of sufficient importance for 
classificatory purposes. Professor Hyatt retains the name Vesti- 
nautilus for the shells comprised in the present group which he 
redescribes, but as Eyckholt’s name cannot be used in the sense 
intended by its author, it is better that it should be suppressed 
altogether. 
^ This is mi eiTor, caused probably by M'Coy’s figure of Discites flanoter- 
yatus (type of the genus) being represented with a closed umbilicus; it is really 
open, both in this and in other species of the group. 
- Some of these can no longer be included in the present genus. 
^ Faune du Calcaire Caibonifere de la Belgique (Annales du Mus. Roy. 
d’Hist. Nat. de Belgique, tom. ii.), 1878, pt. i. p. 86. 
