ORTHOCERAS. 135 



spending in number with the septa, and crossing the shell in a boldly curved oblique 

 line ; the whole of both rings and interspaces crossed by about thirty regular promi- 

 nent threads, which usually have more or less distinct indications of a subsidiary 

 series of less prominent lines between them. Siphuncle central. 



Size. — A typical example of the septal part of this shell in the Museum of 

 Practical Geology, which is 89 mm. in length, measures 17 mm. by 15 mm. in 

 section at its upper end. 



Locality. — Wolborough. This beautiful and highly ornamented species appears 

 to have been common. There are eight specimens in Mr. Vicary's Collection, eight 

 in the Museum of Practical Geology, four in the British Museum, one in the 

 Battersby Collection of the Torquay Museum, and one in the Bristol Museum. I 

 have not met with Sowerby's or Phillips' figured specimens, but their figures exactly 

 correspond with these fossils. 



Bemarhs. — There seems to have been a considerable amount of variation in 

 this species, both in the prominence and frequency of the rings and in the obscurity 

 or occasional absence of secondary threads, and perhaps also in other features. It 

 appears, however, to be distinguished, besides by other features, by the defined 

 character of its rings, which rise almost suddenly from the flattish interspaces. 

 Although rarely, if ever, seen, it is probable that the surface was covered by fine 

 concentric striae in addition to its other markings. The only direct evidence of 

 this is one of Mr. Lee's specimens in the British Museum, which, while wanting 

 the secondary series of longitudinal lines, is covered by very numerous fine and 

 regular transverse threads. The locality of this specimen, however, is not given, 

 and I do not think it came from Devonshire. 



The obliquity of the rings is peculiar. It appears to lie along the shorter axis 

 of its section, and thus suggests that this was the dorso-ventral direction, and 

 consequently that the shell was transversely dilate. The section appears to have 

 been circular near the apex and only to have become elliptic as the shell increased 

 in growth. 



Affinities. — The specimen from Lummaton, described under the name of 0. oryx, 

 presents some similarity to the present species, but is to be distinguished by its 

 prominent transverse striation, its very elliptic section, and some other features. 

 0. suh-tubicinella is separated by its much more numerous rings and by other points 

 mentioned under that heading. 



0. annulatum, Sow.,^ is distinguished from the present shell by its more distant 

 ribs, its numerous sharp, undulating, transverse threads, and the indistinctness 

 of its longitudinal markings. 0. dulce,^ Barrande, has no longitudinal marks, and 

 the transverse threads are generally river-Hke. It is also often slightly arched in 



1 1816, Sowerby, ' Min. Conch.,' vol. ii, p. 73, pi cxxxiii. 



3 1868, Barrande, ' Syst. Sil. Boheme,' vol. ii, pt. 3, p. 321, pi. ccxciv, figs. 1—14 ; pi. ccxcv, figs. 1 

 —29 ; pi. cccclxxxviii, fig. v, 1—3, Et. D (colony) and E. 

 18 



