BELLEROPHON GLOBULUS. 53 



Perner 1 quoted the definition of the genus given by Ulrich and Scofield, 2 

 which restricts its scope to a considerable extent. But not only Ordovician and 

 Silurian, but Devonian, Carboniferous and Permo- Carboniferous species are 

 included by these American authors in this genus, though it seems capable of 

 further subdivision. Perner divides the Bohemian Ordovician and Silurian 

 representatives into three sections or subgeneric groups, their criteria being the 

 length of the dorsal fissure behind the emargination, the size and depth of 

 the umbilicus, the shape and direction of the lateral lips (apertural lobes) 

 of the mouth and the character of the sculpture of the surface. These three 

 divisions are named Sphasrocyclas, Coelocyclus and Prosuptychus, and are 

 characterised as follows : 



(1) Sphaerocyclus- Traces of spiral sculpture on surface; dorsal slit relatively 

 long (about one-third the length of the whorl); mouth not enlarged; slit-band 

 broad; umbilicus deep without callosity. Type H. bohemicus, Barr. 



(2) Ooelocyclus. — Shell spherical ; umbilicus very deep, wide, open, exposing 

 inner whorls; slit-band broad, elevated; umbilical edge (sides of whorl) subangular 

 to angular. Type B. mrissimus, Barr. 



(3) Prosoptychus. — Last half of outer whorl ridged, more or less straightened, 

 laterally enlarged; apertural lobes surround or conceal umbilicus. 



The spiral sculpture on Spfiaerocyclus recalls Bucaniopsis, which seems to have 

 a greater warrant for generic rank than Sphserocyclus. The genus separated off as 

 Cyrribularia, Koken, owing to the infolding of the apertural margins, which is 

 not mentioned by its founder as characteristic, may otherwise be only a subgeneric 

 group of Belter ophoiK 



It is not possible to refer all the British species to one or other of these 

 subgeneric divisions, principally on account of our imperfect knowledge of their 

 characters; moreover, it is possible that other new groups should be formed to 

 receive some of them. 



1. Bellerophon globulus, Lindstrom. Plate IX, figs. 12, 13. 



1873. Bellerophon <H/<thifus, Sowerby, Salter, Catal. Cauib. Silur. Fuss. Woodw. Mus., p. 157 



(a/877) (non B. dilatatus, Sowerby, 1839, in Murchison's Silur. Syst.). 

 1884. Bellerophon globulus, Lindstrom, Silur. Gastrop. Pterop. Gotland, p. 75, pi. v, figs. 25-34. 



Specific Characters. — " Shell of somewhat variable form, globular, ovate or 

 elliptical in outline ; surface of a dark glossy hue, almost smooth, with extremely 

 fine, densely-packed transverse striae, which join the slit-band at an angle of 38°, 

 bend outwards towards the sides and again converge towards the umbilicus. 



1 Perner, op. cit., pp. 130, 131. 



2 Ulrich and Scofield, op. cit., p. 853. 



