450 Dr. Wheelton Hind — British Carhoniferous Goniatites. 



Height of last whorl about half the diameter. Whorls ?4, oval in 

 section, broader than high, indented by preceding whorl. Umbilicus 

 with somewhat raised and rounded margin and convex inner area, 

 iufandibuliform. Periphery very convex, marked off, in casts, from 

 the lateral area by a spiral groove. Body-chamber occupies almost 

 a complete whorl. Test unknown except on inner area of umbilicus, 

 where there are many distinct, close ribs. The cast shows indications 

 of numerous strong carved ribs, with a deep sinus backwards on the 

 periphery. Suture-line as figured (PI. XVI, Pig. 13^). 

 Dimensions. — Diameter, 43 mm. ; transversely, 17 mm. 

 Locality. — Hedesdale Ironstone, Northumberland. 

 Observations. — Hitherto this shell has always been confused with 

 G. truncatum, Phillips, from which it differs essentially in the shape 

 of the periphery, which is less angular, the lateral area is less 

 compressed, and possesses a spiral groove. The suture, too, has 

 marked differences in the central saddle and peripheral lobe. 



The late J\Ir. Crick pointed out to me that Fig. 13, PI. XVI, shows 

 an interesting condition of growth. The last septum is perfectly 

 formed («), a second septum was being formed (b), and a third 

 septum is faintly indicated by a line forming the boundary of the 

 muscle attachment. The sudden rise forward of this line indicated 

 the commencement of the shell muscle. The spiral line on the left 

 side of the shell is half an inch away from the margin of the 

 umbilicus, while that on the right is much closer, only a quarter 

 of an inch away. A younger specimen shows no spiral groove at 

 all, so it probably is only an old-age character. 



EXPLANATION OP PLATE XVI. 

 Fig. 



1. Sagittoceras acutum, sp. nov. § nat. size. 

 la. Id. The suture-line, f nat. size. 



lb. Id. In profile. §- nat. size. 



2. Pericyclus divaricatuvi, Hind. § nat. size. 

 2a. Id. In profile, f nat. size. 



3. Id. Showing the ornament, f nat. size. 



4. Id. The young stage. 

 4<x. Id. In profile. 



5. Id. The ornament and orifice in adult. § nat. size. 



6. Id. The suture-line. § nat. size. 



7. P. virgatus, de Koninck. f nat. size. 

 la. Id. In profile. § nat. size. 



8. P. inipressus. Showing the ornament. x 2. 

 8a. Id. In profile, x 2. 



9. Id. Cast. 



9a. Id. In profile. 



10. Id. The young stage, x 4. 



12. Id. Side view showing the ornament. x 2. 

 12a. Id. In profile, x 2. 



126. Id. The suture-line. x 2. 



13. P. redesdalensis. Showing (a) last suture completely formed, (b) new 



suture commencing, (c) line forming the boundary of the muscular 



attachment. | nat. size. 

 13a. Id. In profile. 

 136. Id. The suture-line. 



