558 Karl A. Grünwall. 



there been a richer and more complete material at our command it 

 would, perhaps, have been possible to classify this North-east Green- 

 land form as a variety of the species in question. 



The greatest difference is that our form has a greater length, 

 with more acute-angled outline of the shell, a narrower beak and 

 less thickness. In order to accentuate this difference we shall, be- 

 low, compare the dimensions of our specimen and of Tschf.rny- 

 scHEw's PI. 60, Fig. 2, although it should be remarked that our spe- 

 cimen is somewhat younger, which may, to some extent, be the 

 cause of these divergences. 



C. Karpinskii TscHERN. PI. 60, Fig. 2 : length 19, width 22, thickness 17 mm. 

 С cfr. Karpinskii — 15, — 15, — 12 — . 



In our specimen the surface of the shell is desquamated in the 

 umbonal region, so that the sculpture is not quite distinct, but the 

 ribs are otherwise the same, with the exception that thej^ are some- 

 what narrower, which, possibly, may depend on the lesser width of 

 the shell, or also from the fact that an indication of a fifth pair of 

 ribs can be distinguished on the lateral portions of both valves. The 

 sinus of the ventral valve can first be observed at about the middle 

 of the valve, but the median ribs of the dorsal valve appear as 

 such already above the middle of the valve. 



С Karpinskii Tschern. occurs in the Urals in the Schwagerina 

 horizon. 



N:o 3. Athyiis Royssii L'Eveillé. 



For synonyms see Waagen, 1882—84, p. 475. 



It is with hesitation that 1 venture to refer two specimens from 

 the light, fine-grained limestone, N:o 15A, from the Mallemukfjæld, 

 to the above-mentioned species, respecting whose difference from 

 A. pectinifera Sow. there exists some doubt. 



TscHERNYSCHEW, 1884, p. 290, has expressed himself in such a 

 manner that one can understand that he is most inclined to identify 

 these two forms as one species, but in 1902, p. 102, he gives them 

 as separate species, and notes several distinctive features between 

 them, in addition to that of size in general, viz., the absence of a 

 sinus in A. pectinifera ; the straighter hinge-line, the more powerfully 

 developed beak, with a larger foramen, and the finer and closer- 

 lying spines on the striae of growth in .4. Royssii. 



Waagen, on the whole, follows Davidson's views respecting the 

 difference between these two species, and considers that the smaller 

 form where not even an indication of a sinus in the ventral valve 

 is seen, should be classified as A. pectinifera. 



