566 Karl A. Grönwall. 



related to each other, that, in many instances, it is difficult to dis- 

 tinguish them from each other, and a thorough revision is probably 

 required, especially of the 3 species, Sp. supramosquensis Nik., Sp. 

 Fritschi ScHELLw. and Sp. Nikitini Tschern. 



The specimens from North-east Greenland which are at my dis- 

 posal are not so well preserved that they can throw any light over 

 the other species, but I have to be contented with establishing their 

 proximate relationship with Sp. supramosquensis, and their difference 

 from the other forms, such as these have been described. 



They are fairly easily distinguished from Sp. mosquensis, first 

 by the dental plates and secondly by the sculpture. 



As shown by Fig. 16, the dental plates, which are almost straight, 

 do not reach farther in the shell than to somewhat beyond its 

 middle, while those of Sp. mosquensis, where the plates form convex 

 arcs with the median line of the shell, reach to ^/4 or ^/5 of its length 

 The best illustrations of the interior of Sp. mosquensis, which are 

 found, both in Trautscholu (PI. XXXVII, Fig. 1—2), and in Frech 

 (Lethæa palæozoica, PI. 47 a, Fig. 5 as new figures after Trautschold's 

 original), are in want, both of any statement of dimensions or of 

 any hint as to the outline of the complete shell, so that, by their 

 help, it is only possible to give an approximate estimation of the 

 relative length of the dental plates. De Koninck (1883, p. 381, PI. 

 XIV, Fig. 11), states that the dental plates reach almost to the ante- 

 rior margin of the shell, and his figures show this. Holtedahl's 

 statements point in the same direction. 



The sculpture, as is seen by Fig. 14, shows dichotomy in the 

 case of several of the ribs, which is not the case with Sp. mos- 

 quensis. 



We meet with greater difficulties, on the other hand, when 

 endeavouring to decide whether our specimens shall be referred to 

 Sp. supramosquensis, Fritschi or to ^Чkitini; between the first two of 

 these species, especially, the difference has not been very clearly 

 pointed out, and it is only gradually that this has been done. Spi- 

 rifer Fritschi was established as a distinct species by Schellwien 

 (1892) but, later on (1894, p. 75, Foot-note), the same author has 

 expressed his doubts as to the correctness of giving Sp. Fritschi as 

 a distinct species, and has supposed it to be identical with Sp. supra- 

 mosquensis. In Lethæa palæozoica (1897 — 1902) Frech takes these two 

 species as identical, so that his comparison between Sp. mosquensis 

 and Sp. supramosquensis Nik. cannot be admitted as evidence. As 

 far as I can see, Frech, for his figuring of the latter, has probably 

 employed both Sp. supramosquensis and Sp. Fritschi as originals (PI. 

 47 b, Fig. 1 a ; and the Fig. in the text, p. 260, Sp. Fritschi from the 



