214 



size as the Chinese fossils, so that they cannot be descriminated from the 

 latter when the two are mixed tog-ether. Two of such specimens are pictured 

 on one of the plates in this paper for the sake of reference. 



In all essential points the Chinese fossils are really nothing but AtJtyris 

 royssii : all the peculiarities that separate the species from any of the allied 

 species will equally distinguish the Chinese species from those latter. The 

 only thing that cannot be left unmentioned is that none of the Chinese 

 specimens possess spines on the conentric growth lines or lamellse on the 

 surface of the shell. The species seems to be characterized by this feature 

 with several other points, for Davidson remarks that Athyris royssii is 

 distinguished from a very closely, allied form, AtJtyris planosiilcata, by its 

 spines, which are very different from the surface sculptures of the latter.-'' 

 SoMMER even identified a fossil from the Culm of Konigsberg bei Giessen 

 with this species on account its possessing such spines."^' Such minute things 

 as spines, however, are preserved in the fossil state only in very rare cases. 

 It is not an every-day thing that one should find the spines of any Prodiictus. 

 The same must also be true of the surface ornamentations of "CixQ. AtJtyris. 

 In reality, it seems that there have been very few examples ever discovered 

 with the details of the surface features preserved uninjured ; there are very 

 few records of such fossils. In reality, however, there are a few specimens 

 among the materials from China that have radial ribs upon the concentric 

 lines. 



As Waagen'^ lias remarked this species is very variable with regard to 

 tjie degree of the development of the median fold of the shell. According to 

 De Koxinck the dorsal valve has a median fold which occupies in adult speci- 

 wiens not more than the anterior half of the shell ; this fold corresponds to a 

 sinus " assez profond de la valve opposee."'^' Davidson, however, says, in 

 his diagnosis of the species, The valves are almost equally and uniformly 

 convex up to a certain age, after which a broad mesial fold of greater or 



1) Davidson:— Monogr., p. 185. 



2) Sommer: — )oc. cit. 



3) Waagen: — op. cit., p. 475. 



4) D.';. KoNiNCK: - op. cit.. p. 85. 



