SPIRIFERA. 155 



similar in ornament from Chimay, in Belgium), while others are referred to Cyrtia 

 Murchisoniana (one of these being the figured Chinese specimen 1 of it). While 

 the extreme forms of these shells seem perfectly distinct, I have failed to find any 

 definite line of specific division between them. Though they vary much in shape, 

 some being longer, more ovoid shells, and having a shorter hinge-line than 

 any European forms, they may be traced without break into the ordinary forms 

 of the shell, and even on to those alate forms with produced wings. Their 

 styles of minute ornament, which is often perfectly preserved, are not 

 constant to particular shapes, though in the elongate form, in which a foramen 

 is sometimes seen, this minor ornament generally consists of fine longitudinal 

 threads, and in the broad form generally of transverse lines or of coarser longi- 

 tudinal threads irregularly broken into spines, similar, in fact, to the Russian 

 figure, and thus approaches the texture seen in our specimens from Snapper 

 Quarry. In the Museum of Practical Geology is a specimen from South Petherwyn 

 with the same structure as these Snapper specimens, which have narrow areas. 

 That shell has a large flattish receding area, and a slightly incurved umbo, and 

 evidently falls within the variety Sp. Barumensis. Lastly, in the Woodwardian 

 Museum is a slab from South Petherwyn, with three specimens, which show trans- 

 verse rows of punctations with a tendency to run into longitudinal lines, thus 

 connecting our two figured examples from Ashford and Snapper ; and, moreover, 

 the ornament in these three specimens is of three different degrees of coarseness, 

 intermediate between those of the two last-mentioned shells. 

 It would thus appear 



(1) That the various styles of ornament here described are not inconsistent 

 with each other, and may all belong to Sp. Verneuilii, and consequently that 

 Sp. Verneuilii is as variable in ornament as in shape. 



(2) That though it is still possible that more than one species may be included 

 under this name, there is no evidence of this from our Devonshire specimens ; even 

 the form Sp. Barumensis, distinctive as it sometimes seems, does not appear to have 

 any definite characters for its separation. 



(3) That the variations of Sp. Verneuilii are remarkably great. It might 

 possibly be described as " a species in process of solution." While I venture to 

 think that the difficulties to certain developments of evolutionary theories which 

 are in vogue at present may ultimately be found to be insurmountable, we may say 

 that if species have changed at all it is probable that there were times when the 

 forces of variation were especially active. Every now and then we meet with a 

 species which is so variable that it seems impossible to say whether it is one or a 

 collection of forms. This may be a permanent state, or it may be the crisis in its 

 life-history where it is breaking up into a number of new species. The variations in 



1 Davidson, ' Quart. Journ. Geol. Soc.,' vol. ix, 1853, p. 355, pi. xv, figs. 6-9. 



