EXPLANATION OF THE PLATES AND WOOD-CUTS. 



A handsome shell an inch in diameter. 

 Loc. Petherwin ; Landlake, Cornwall. 

 Fig. 17. Terebra nexilis. Subulate, acute, longitudinally striated ; whorls flat; striae 

 gently bent twice. 



A neat shell, much resembling Rissoa Lefebvrei (Leveille in Mem. de la Soc. 

 G^ol. de France, vol. ii. part 1, p. 40, PI. IL fig. 25) ; but the striae are finer, the 

 shell more elongated, and the sides of the whorls flatter, than in the specimens we 

 have examined of that fossil. 

 Loc. Petherwin (frequent). 

 Fig. 18. Goniatites vinctum. Discoid ; inner volutions two-thirds exposed ; sides of 

 the whorls flat ; their inner edges abrupt ; front rounded, encircled by a thread-hke 

 keel ; inner whorls crossed by straight undulations ; lobes of the septa three on 

 each side, that on the middle of each side by far the longest ; ovate, pointed. 



The specimen before us, though very imperfect, is clearly distinguished from 

 G. Henslowi (M. C. t. 292), by having but three instead of four lobes on each side ; 

 and from G. subarmatus, (Munster, Plan, und Goniat. Tab. VL f. 2.) to which it 

 is closely allied, by the ovate form of the lobes, which in that fossil have their sides 

 straight, and the whorls in that species do not increase so rapidly. 



We have had the good fortune to see, in the Rev. Mr. Williams's rich collection 

 of Cornish fossils, several new and interesting species of Goniatites and Cly- 

 menia in company with a species resembling Nautilus {Goniatites'^.) complanatus 

 (M. C. t. 261.), which he has however reserved for future publication. 

 Fig. 19. Clymenia {Endosiphonites, Ansted) IcBvigata. {Planulites Icevigatus, Munster, 

 Plan, und Goniat. T. I. f. 1.) A large smooth shell, with many whorls, and only a 

 slight sinus on either side of each septum. Our specimens are not so large as that 

 figured by Count Munster, nor is the wave in the septum placed so near the front 

 of the whorl. 

 Fig. 19 a. Clymenia linearis. {PL linearis, Munst. loc. cit. T. IL f. 5, 6. Endosiphonites 

 carinatus and minutus. Ansted Camb. Phil. Trans, vol. vi. PI. VIII. f. 1, 2, 3.) 



This well-marked species is abundant in the Petherwin beds, and is distinguished 

 from the preceding by the deep acute-angled sinus in the side of the septum, and 

 also by its striated surface and Hnear keel. 



Having examined the Cambridge specimens, we can see no reason for supposing 

 the E. minutus a distinct species, especially as we have found on it the charac- 

 teristic keel of E. linearis, or for altering the original specific name given by Count 

 Munster. 



Loc. Petherwin. 

 Fig. 20. Orthoceras striatulum. Rather rapidly tapering, ornamented with prominent 

 transverse rings, crossed by numerous fine threads, which alternate with still finer 

 lines ; annulations sharp, oblique, rather more distant than the septa. 



This has a close affinity with Orthoceras Tubicinella of the Plymouth limestone 

 (PI. LVII. f. 29.) ; but the threads are closer and finer, and it appears to be a 

 larger species. At first sight it looks much like C. annulatum (M. C. t. 133.) ; but 

 the longitudinal lines, and want of transverse scales, easily distinguish it. 



