82 DEVONIAN FAUNA. 



later plate Barrande figures some large casts which present very little signs of 

 tubercles, but show that the aperture was almost closed, and that the lip possessed 

 two lateral sinuses corresponding in position to the spines, instead of having a single 

 sinus on the back ; and thus that it differs generically from the present species. 

 He also gives a doubtful variety, irregulare^ which approaches the genus Gijroceras 

 in having a slightly open spire. 



II. Family. — Teoohocbeatid^. 

 1. Genus. — Teochoceras, Barrande, 1848. 



This genus was founded by Barrande for a group of the Nautiloidex, which 

 have oval or circular chambers loosely coiled in few volutions, which do not lie in 

 one plane. As a rule the volutions are not contiguous, and the asymmetry is 

 sometimes very considerable. The aperture is simple. The siphuncle is situated 

 somewhere between the centre and the ventral margin, but not, as a rule, close to 

 the margin. The shell is usually covered with transverse rings, inclining back- 

 wards, and crossed by finer spiral striations. It belongs to the Upper Silurian 

 and Devonian formations. 



Under this genus I have classed two groups of shells, neither of which can be 

 regarded as certainly belonging to it, but which at the same time appear to agree 

 better with its characters than with those of any other genus. In both the 

 asymmetry is very small, but both have decided affinities to Bohemian shells 

 placed by Barrande under this genus. The first group consists of a single 

 English Devonian species, Tr. Foordianum, and may be classed with Tr. arduense 

 (Stein.), 'Ir. interstriale, Barr., and Lituites cornu-arietis, var., Portlock, (not 

 Murchison). These species agree in the character of both major and minor orna- 

 mentation. The second group contains four (or perhaps five) Devonshire forms, 

 Tr. Vicarii, Tr. pulcherrimum, Tr. ohliquatum (Phil.), and Tr. reticulatum (Phil.), 

 besides several Continental, as Tr. mvMistriatum (F. Rom.), Tr. tenuisquamatum 

 (Sandb.), and Tr. nodosum, Barr. These form a very definite and compact group, 

 having many points in common, as, for instance, the character of the major and 

 minor ornamentation, the slight asymmetry, the squarish shape of the section of 

 the whorls, and the position of the siphuncle about half way between the centre 

 and the circumference. Whether they should be regarded as a sub-genus of 

 Trochoceras or of Gijroceras is not very certain. Barrande included the Bohemian 

 species under the genus Trochoceras, but Mr. Foord is more inclined to regard 

 them as belonging to Gijroceras ; and this is supported by the fact, that, as we 

 1 1865, Barrande, ' Syst. Sil. de Boheme,' vol. ii, p. 153, pi. xliii, figs. 1—7, Efc. G. 



