﻿BRITISH FOSSIL CEPHALOPODA. 85 



marked in the small specimen. They are about 3° oblique to the general diameter, but 

 run rather irregularly, and their closeness varies : at the small end of the small speci- 

 men they are very close, and end by being -^ T the preserved diameter apart ; in the 

 large specimen they are closer at the large end, where they are at -^ the flattened 

 diameter apart. The surface is covered with an irregular granulation, something 

 like shagreen. No septal or siphuncular characters are certainly seen ; but towards 

 the larger end, at a diameter of 2^ inches, there are depressed bands, as if a rect- 

 angular piece of tape had been impressed on the surface, leaving lines which might 

 be taken for sutures. The large specimen attains a diameter of 3^ inches. From the 

 Bala Series of Desertcreat. In the Museum of Practical Greology. 



General Description. — There are no specimens known which give better characters 

 than the type, but the number and strength of the ribs remain the chief features of 

 the species. The specimens referred by Salter to a new species under the name 

 0. encrinale show no more than this, though the ribs have a maximum of strength. 

 At the best the whole series form a doubtful species, as it would run close to others 

 if the surface were well enough preserved to show any minor ornaments. A specimen 

 from Bala Limestone, in the Museum of Practical G-eology, labelled 0. multiannulatum, 

 which appears to belong here, has an oval section, and the siphuncle seems to be 

 midway between the centre and the circumference on the long diameter. 



Relations. — From 0. arcuoliratum this differs by the number of the ribs, and 

 from 0. velatum by their less rounded character and greater irregularity. 



Distribution. — In the Bala Beds of Desertcreat (5), of Bala (1), of Llandeilo (1), 

 and Wrexham (1) ; also in the Lower Llandeilo of Shropshire (2) [0. encrinale~\. 



Orthoceras gracile, Portlock, PI. III. figs. 5, 5a; 9, %a, 9b, 9c. 



1843. Orthoceras gracile, Portlock, 'Geol. Eep.,' pi. 25, fig. 2, p. 366. 

 Syn. 1843. Orthoceras tubicinella, Portlock, ' Geol. Eep.,' pi. 25, fig. 34. (Not of Sowerby.) 

 1843. „ calamiteum, Portlock, 'Geol. Eep.,' pi. 25, fig. 1. (Not of Minister.) 



1851. „ ,, Salter in Murchison's "Silurian Eocks of Scotland," Quart. 



Journ. Geol. Soc, vol. vii. p. 173. 



1851. Orthoceras anellum, M'Coy in Sedgwick's " Geological Structure of the Frontier 



Chain, &c," Brit. Assoc. Eep. p. 103. (Not 0. annellatum of Hall.) 



1852. Orthoceras bilineatum, M'Coy, ' Palaeozoic Fossils,' p. 319. (Not of Hall.) 

 1857. „ „ Salter in Murchison's ' Siluria,' Foss. gr. 42, fig. 2. 



Type. — The original specimen described by Portlock under this name is a surface 

 fragment ; the section is therefore unknown. The rate of increase is very slight, but 

 incapable of measurement. The ornaments consist of rounded undulations with an 

 obliquity of 3°, of such a character that their interspaces are simply re-entering 

 angles ; they tend to die away towards the larger end, and are distant i the diameter. 

 These are crossed by light longitudinal ribs, distant about ^ the diameter, or half 



