112 DEVONIAN FAUNA. 



Size. — Length, 55 mm. ; ventro-dorsal diameter of body-cliamber, 29 mm. ; 

 lateral diameter about 26 mm. 



Localities. — From Wolborough there are four specimens (of which one is a 

 large but doubtful fragment) in the Museum of Practical Geology, and two in 

 Mr. Vicary's Collection. From Lummaton there is a specimen in my Collection. 



Bemarhs. — The recurved pyriform contour and delicate ornamentation distin- 

 guish this species. Unfortunately the examples of this, as of some of the 

 neighbouring forms, are peculiarly defective, and it is a matter of extreme 

 difficulty both to discern their true characters and to determine their specific 

 identity, and even to define their generic position. Thus the only specimen of 

 those above mentioned which shows any indication of the siphuncle is one in the 

 Museum of Practical Geology, which is a fragment showing the ventral part of 

 the body-chamber, which is defective in the other specimens, and which therefore 

 cannot be looked upon with any degree of certainty. Several of the specimens 

 give evidence that the oral aperture was evidently much constricted, but its exact 

 shape is impossible to surmise. 



Affinities. — Phragmoceras rimosum, Barrande,^ tapers more rapidly, and has 

 more convex lateral outlines. Its ornamentation also seems less distinct. 



Gyrtoceras corniculum, Barrande,^ has a more arched outline on the concave 

 side, and more expanded aperture. Phragmoceras imhricatum, Barrande,^ is not 

 contracted dorsally round the mouth, and is more arched. Its markings also are 

 not so sharp. 



V. Family. — Gomphoceeatid^. 

 1. Genus. — Poterioceeas, M'Goy, 1844. 



This genus is divided from Gomphoceras by its simple and less contracted 

 mouth, its slight tendency to an arched form, &c. The siphuncle is subcentral or 

 marginal and beaded between the septa. In two of the three species described below 

 it is situated at the ventral margin of the shortest diameter of the elliptic section. 

 The genus extends from the Lower Silurian to the Carboniferous. It was founded 

 by M'Coy* for a Carboniferous species, but was treated as a synonym of Gom- 



1 1865, Barrande, ' Syst. Sil.,' vol. ii, p. 230, pi. xlviii, figs. 1—7, and pi. xcviii, figs. 5—9, £t. E. 



2 1866, ibid., vol. ii, p. 492, pi. cxxi, figs. 1—23, Et. E. 



'■'' 1865, ibid., vol. ii, p. 212, pi. xlvi, figs. 1 — 12; pi. clxxv, figs. 1 — 15, and pi. ccxvii, fig. 5, Et. E. 

 * 1844, M'Coy, ' Sjnop. Carb. Foss. Irel.,' p. 6. 



