1815.] On the Orthoceratites of Scotland. 20J 



I consider this as the orthoceratites sjiperficie sulcata of Ure, 

 pi. xvi. fig. 2. The waving of the ridges he does not mention • 

 but he observes, that the shell " is finely striated in the same 

 direction with the sulci." 



7- 0. U'ldala. — Shell, tapering ; ridges, waved and smooth; 

 pipe, small and central. Fig. 7- 



This specimen is one inch and two tenths in length, seven-tenths 

 in diameter at the base, and upwards of five-tenths at the apex ; 

 the ridges arc 1 1 in number, more deeply waved, and less numerous, 

 than the preceding species; there is the appearance of an epidermis, 

 of a black colour, and obscurely striated ; where the shell is 

 exposed, both the ridges and the grooves are perfectly smooth. An 

 imperfect specimen of an eschara adheres to the shell. 



8. 0. Annularis. — Shell, subcylindrical ; ridges, distant, nearly 

 even, and smooth. Fig. 8. 



The largest portion of this shell which I possess is about an inch 

 in length, and upwards of three-tenths of an inch in diameter; the 

 ridges are nearly one-eighth of an inch asunder, and are more 

 obtuse than the preceding. In the spaces between the ridges there 

 are at least two chambers. 1 have not been able to observe the 

 pipe, as all the specimens are much incorporated with the lime-stone 

 in wliich they are imbedded. 



J). O. Rugnm. — Shell, subcylindrical ; ridges, waved and 

 tuberculated, witli longitudinal lines ; pipe, minute and lateral. 



Fig; 9. 



The length of this specimen is upwards of an inch and a quarter, 

 and the breadth about six-tenths. The ridges are formed into knobs 

 by faint longitudinal lines, which cause the intermediate spaces to 

 exhibit a grooved appearance ; they are upwards of two-tenths of 

 an inch asunder, and contain two chambers in the interval ; the 

 pipe is very small, and placed close by the edge. 



C. Surface of the Shell with Longilzidinal Planes. 



10. 0. ylngularis. — Shell, nearly cylindrical, angular, with 

 about IG smooth longitudinal planes; pipe, small and lateral. 

 I'ig. 10. 



1 ixjssess about half an inch of this shell, which is nearly of equal 

 thickness, scarcely exceeding the tenth of an inch in diameter. 



There is a portion of a triloiite adhering to the lime-stone in 

 which this ahcll is imbedded. It resemi)les in its general appearance 

 the .>-pccies from Dudley, in Shropshire, figured in I'arkinson's 

 Organic Remains, vol. iii. tab. xvii. fig. 1 1. 



II. — CHEMICAL HISTORY. 



The original shell appears still unchanged in species .G, G, and 7» 

 of a thin and very delicate texture ; hut in the remaining sjiecics 

 tl»e original structure is completely altered. In general, the sliell and 

 the partitions are changed into fibrous or granular limc-stonc, the 

 chaniljcrs occupied with crystals of quarlr and lime-spar, and the 



