84 DEVONIAN FAUNA. 



located, altboiigh from the number and contiguity of the whorls it must be 

 regarded as an aberrant form. 



Affinities. — To Tr. arduense (Stein.) it evidently is closely allied, but on com- 

 paring it with Steininger's original figure it is seen to be separable from it, as the 

 curvature is greater, and the number of ribs very much less. Tr. interstriale, 

 Barr.,^ seems to come much nearer, and has longitudinal markings like those 

 indicated in our shell. It differs, however, in being a stouter shell with a circular 

 coil and rather more numerous ribs. Tr. placidum, Barr.,^ and Tr. trocJioides, 

 Barr.,^ are still stouter and much more asymmetrical, and these also want 

 the elliptical coihng. All the other Bohemian species which at all approach it 

 are clearly distinguished by the much greater number of the ribs, besides other 

 differences. The figure which Portlock* gives of Lituites cornu-arietis (var.), 

 Murchison,^ has much closer ridges, has secondary striae, and is larger and much 

 flatter. There appears, however, a generic identity, and it is stated by Blake® to 

 be undoubtedly a TrocJioceras. 



The Bohemian species of Lituites and Ophidioceras are all totally difierent, and 

 prove that our Devonian shell belongs to neither of these genera. Ophidioceras 

 articulatum (Sowerby)'' has a circular and not elliptical spire, and direct ribs with 

 only a slight backward direction towards the outside. That genus appears 

 characterised by a ventral band, of which there is no trace in the present fossil. 



II. Group of Tr. ohliquatum. 



Spire loosely coiled, of few whorls, not contiguous. Section sub-quadrate, 

 broadest ventrically. Siphuncle situated on the ventral side between the centre 

 and the ventral margin, generally midway between them. Chambers rather broad. 

 Whorls with parallel transversely oblique ridges, often becoming nodes on the 

 ventral elbow ; surface ornamented with a fine network formed by numerous 

 small longitudinal ridges crossed by finer transverse lines. 



1 1865, Barrande, ' Syst. Sil. Bohem.,' vol. ii, p. 107, pi. xv, figs. 1—7, Et. E. 



2 Ibid., p. 112, pi. xxiii, figs. 1—4, Et. E. 



=* Ibid, p. 116, pi. xxix, figs. 16—26, Et. E. 



* 1843, Portlock, ' Eep. Geol. Londonderry,' p. 383, pi. xxviii b, fig. 7. 



5 1830, Sowerby in Murchison's ' Sil. Syst.,' p. 643, pi. xx, fig. 20. 



6 1882, Blake, ' Mon. Brit. Foss. Ceph.,' pt. 1, p. 217, pi. xxi, fig. 6, and pi. xxviii, fig. 5. 



7 1830, Sowerby in Murchison's ' Sil. Syst.,' p. 622, pi. xi, fig. 5, and 1882, Blake, ' Mon. Brit, 

 Eoss. Ceph.,' pt. 1, p. 230, pi. xviii, figs. 14, 15. 



