TROPIDODISCUS. 69 



1884. Bellebophon bisxtlcatus, Beushausen. Abhandl. Geol. Specialk. Preuss., 



vol. vi, pt. 1, p. 45, p]. ii, fig. 3. 

 1893. — — ? Collins. Trans. Eoy. Geol. Cornwall, vol. xi, 



p. 38. 



Description. — Shell very small, not quite horizontally symmetrical, wider than 

 high. Spire rapidly increasing. Umbilicus very large. Whorls deeply convex 

 on the shoulder, then becoming concave till they rise in the central part into a 

 large elevated convexity, and returning with the same sweep reversed to the 

 umbilicus. Surface quite smooth, with no signs of sinus-band or ornament. 



Size. — Height 7 mm., width 8 mm. 



Localities. — In the Museum of Practical Geology are two specimens from 

 Baggy Point and one from West Angle Bay, Pembrokeshire; and in the Wood- 

 wardian Museum one from west of Saunton Court. 



Remarks. — Whether B. trilohatus, Sowerby, is a long-lived and variable species, 

 or whether there are several distinct kindred forms bearing the same facies, is a 

 question on which I have not yet been able to arrive at a satisfactory conclusion. 



As figured by Sowerby and F. A. Romer, B. trilobatits is a much more globose 

 form. Sandberger gives three varieties, acutus, typus, and tumidus ; the first 

 almost flatly discoidal, the second corresponding to B. hisulcatus, F. A. Romer, and 

 the third as globose as Sowerby's types. Of these, CEhlert remarks that he has 

 collected all three in Mayenne in the midst of intermediate forms. Again, Phillips 

 gives three varieties from Devonshire, one of which agrees with Sowerby's shell in 

 globosity, and this is apparently the one which he quotes from Baggy. 



Furthermore, the specimens which I have myself seen agree with B. hisulcatus, 

 F. A. Romer, though they do not seem distinguishable from Silurian specimens in 

 the Museum of Practical Geology, with which I have compared them. 



M'Ooy in 1855 separated the Devonshire shell from the Silurian under the 

 name B. hisulcatus, Romer. 



Beushausen in 1884 treated B. trilohatus, B. hisulcatus, and B. tumidus^ as 

 distinct species, while in 1889 Sandberger ^ himself separated B. tumidus from 

 B. trilohatus. In this he is followed by Kayser ^ in 1895, who, moreover, describes 

 a distinct sinus-band with marginal threads on some specimens of B. tumidus from 

 Pepinster, 



The B. trilohatus of d'Orbigny appears exactly to agree with B. hisulcatus^. 

 F. A. Romer, and our specimens. 



On the whole it seems best, at least as a provisional arrangement, to treat 



^ 1884, Beushausen, ' Abhandl. Geol. Specialk. Preuss.,' vol. vi, pt. 1, p. 44. 

 ~ 1889, Sandberger, ' Jahrb., Nass. Ver. Naturk.,' vol. xlii, pp. 13, 25. 

 3 1895, Kayser, 'Ann. Soc. Geol. Belg.,' vol. xlii, p. 182, pi. iv, figs. 5—8. 



