SPIRIFERIDyE. 



121 



Athyris obovata, Souk (sp.). PI. XII, fig. 19; and PI. XIII, figs. 5, 5 «. 

 Atrypa obovata, Sow. Sil. Syst., pi. viii, fig. 9, 1849. 



Terebkatula — Sow.1 Barrande. Silur. Brach. Bohmen, p. 28, pi. xv, fig. 8, 

 1847. 



— — Bav. Bull. Soc. Geol. France, 2nd ser., vol. v, p. 327, 1848. 



Atrypa — Phillips and Salter. Mem. Geol. Surv., vol. ii, pt. 1, p. 2/8, 



1848. 



Athyris? — Salter. Siluria, 2nd edit., p. 542, pi. xxii, fig. 16, 1859. 



Spec. Char. Almost circular, a little wider than long ; valves nearly equally convex, 

 with or without a small rounded elevation or fold near the front in the dorsal valve, to 

 which corresponds a small depression in the ventral valve ; beak small, incurved over the 

 umbone of dorsal valve ; surface smooth, or rather marked by concentric and slightly raised 

 lines of growth. 



Length 5, width 5^, depth 3^ lines. 



Obs. All my efibrts to obtain a sight into the interior of the dorsal valve of this 

 species have proved unsuccessful; but I feel almost certain that it was provided with 

 spiral lamellae. I have received from Dr. HoU the interior of the ventral valve, of which 

 a figure will be found in PI. XIII. British examples of this shell are small, and do not 

 attain the dimensions of the specimen figured from Bohemia by Barrande. I am also not 

 certain whether the species under description and Atrypa compressa, Sow., should not be 

 considered as a single species. It is true that Sowerby informs us that in his A. obovata 

 there exists a small marginal elevation at the front in the dorsal valve, forming a rounded 

 sinus in the ventral ; but, although this may be the case in some specimens, it was not 

 so in many examples that have fallen under my notice, so that I am very much inclined 

 to regard them as one species, or as varieties only but as this does not appear to be 

 the view taken by the generality of palaeontologists, I shall provisionally leave them under 

 separate heads. They present the same dimensions ; but A. compressa is stated to be 

 equivalve, and A. obovata to be inequivalve. 



1 In the 'Annual Report of the Trustees of the Museum of Comparative Zoology,' Boston, 18(j3, 

 Mr. Louis Agassiz states that " The differences noticed among animals of the same species do not con- 

 stitute varieties, but are individual differences, similar to those which may be noticed among the different 

 individuals of the same family among ourselves. Any attempt to group them under a few heads, as 

 varieties, fails as soon as large numbers of specimens are considered. What have been generally described 

 as varieties by naturalists are extreme individual differences, occurring more frequently in certain species 

 than in others ; but, like all others, presenting the same indefinite peculiarities, which forbid one consider- 

 ing them as in any way typical. This shows that individuality constitutes the most prominent feature of the 

 organic kingdom, and is by no means confined to the human family." 



IG 



