66 DEVONIAN FAUNA. 



out by the specimens we have seen. The latter and much smaller species is 

 often deeper in actual measurement than the former, and, if the very small 

 specimen in the Torquay Museum be rightly regarded as a specimen of the 

 present shell, we learn that in the young state it is much less like G. globosus 

 than it is in the adult. At that stage the whorls would appear to increase 

 more rapidly, and to be more regularly convex than is the case in larger shells, 

 and the umbilicus is comparatively smaller. In this state it is almost exactly like 

 G. discus, F. A. Romer, except that the latter is not quite involute, and so shows 

 the inner whorls in the umbilicus. A suture-line of his shell is figured by Romer, 

 which is like what we might suppose G. transitorius, Phil., to have possessed. The 

 similar characters are, however, too slight to make it safe to adopt Romer' s name 

 for the species, especially as it seems to be a similarity between the mature German 

 shell and the young of the British form. 



Affinities. — G. suhnautilimis, von Buch, as interpreted by Sandberger,' is 

 something similar in general shape, but the umbilicus is rather larger, the whorls 

 are rather less involute, and their inner margins are rounded instead of angular. 

 Von Buch's own figures^ of it are poor, but they convey a very different impression, 

 being much more ovoid in section, with more rapidly increasing whorls and an 

 undulated surface on the cast. He certainly states it to be wholly involute, as is 

 the English form ; but his figures and description tend, on the whole, to prove 

 that the two species are distinct. G. carinatus (Beyrich)^ has more sloping sides 

 and a higher and more defined keel. G. reticulatus, Phillips, as given by Romer,* 

 is a more spherical shell with a reticulated surface, and without any flattening on 

 the sides. 



6. GoNiATiTBS ARATus, Wliidhome. PI. VI, figs. 16, 16 a, 



1889. GoNiATiTES AEATUS, WJiidhome. Geol. Mag., dec. 3, vol. vi, p. 29. 



Description. — Shell discoidal, flattened, inclusive, of rather small size, con- 

 sisting of few whorls. Surface smooth (?). Umbilicus rather small, trochiform. 

 Sides of the whorls at first flattened or slightly hollowed, and then gently arching 

 to meet in the deeply convex back ; marked by four deeply impressed sulci, con- 

 sisting of a concave curve tending forward from the inner margin, across three- 



1 1851, Sandberger, ' Verst. Rhein. Nassau,' p. 114, pi. xi, fig. 1. 



2 1832, von Buch., ' Uber Amm. und Gon.,' p. 35, pi. i, figs. 9—11. 



3 1837, Beyrich, ' Beitr. Ehein. Ubergangsg.,' p. 35, pi. ii, figs. 2a— c. 

 1852, F. A. Eoraer, 'Beitr.,' p. 2, p. 94, pi. xiii, figs. 31a, b. 



