﻿BRITISH FOSSIL CEPHALOPODA. 119 



Relations. — This species is distinguished from the rest of the group to which it 

 belongs by its rapid rate of increase and widely-separated direct septa. It is a stout 

 form. It would, however, nearly correspond to 0. cenirale (Hisinger) if the riblets 

 were not undulating. 



Distribution. — In the Bala Beds of Desertcreat (1), Barnne, co. Tipperary (1), 

 Dooree (a more doubtful example) and Kildare (1). 



Orthoceras elongatocinctum, Portlock, PI. XIII. figs. 7, 8, 8a. 



1843. Orthoceras elongatocinctum, Portlock, ' Geol. Eeport,' pi. 27, fig. 2 a, b, p. 372. 

 1860. „ „ Baily, Explanation of Sheet 145, ' Geol. Surv. of Irel.' 



pi. 11, fig. 3. 

 1869. „ „ Baily, ' Characteristic Brit. Fossils,' pi. xii. fig. 10. 



Syn. 1843. Orthoceras subflexuosum, Portlock, loc. cit., pi. 28, fig. 3, p. 318. (Not of 



Minister.) 

 1843. ,, tentjicinctum, Portlock, loc. cit., p. 371. 



1852. „ „ M'Coy, ' Pal. Foss.' p. 317. 



1854. „ „ Salter in Murchison's ' Siluria,' Foss. gr. 42, fig. 3. 



Query 1843. Orthoceras regulare, Portlock, loc. cit., pi. 27, fig. 5. 



Type.— Two specimens are figured by Portlock as types, which differ in some 

 respects from one another, but which nevertheless cannot, with present materials, be 

 satisfactorily separated. The section in both is compressed ; the rate of increase in 

 the one (fig. a) is 1 in 14. The body-chamber cannot well be distinguished from 

 the septal portion. The ornaments in fig. a are acute undulating riblets, with very 

 little obliquity, and distant 9 per line at a diameter of 4 lines ; they show a slight 

 tendency to group in series. In fig. b the ornaments are more undulating and 

 oblique in appearance, and distinctly cross the line of the septa, and are distant 10 

 per line. The septa slope in an opposite direction to the ornaments, and are f to % 

 the diameter apart. No siphuncle is seen. The larger of these has a length 

 of 3^ inches, and a diameter of f- inch. From the Bala Series of Tyrone. In the 

 Museum of Practical Geology. 



General Description. — One example referable to this species has an elliptical 

 section, with diameters in the ratio of 10 to 9. In another they are as 7 to 6. The 

 rate of increase is always small, not greater than 1 in 10. The ornaments would 

 appear to vary according to the direction in which they are seen ; though always 

 undulating, their obliquity is more marked when they are seen to cross the septa, by 

 being viewed on the side ; they are sharp and separate. Better specimens might 

 show that there are two species, as there appear to be amongst corresponding forms 

 of the Upper Silurian, viz. those with more direct and those with oblique riblets 

 crossing the septa, but no satisfactory distinction can now be drawn. The riblets 

 are from 10 to 12 per line, or even 18 in very small specimens. The septa are 



