NeiD Species of Leperditia, 3 



Affinities. — ^The well-known L. halthica, Hismger sp./ bears 

 some points of resemblance to the above-described form, as in 

 the structure of the carapace around the central tubercle ; but 

 the united valves are much thicker, the postero-dorsal angle is 

 sharper, and the central tubercle is more median than in our 

 species. Our fig. 2 is near L. eichivaldi of Schmidt,'^ in general 

 outline, especially in his fig. 29. In L. eichvaldi, however, and 

 the next to be noticed, there is a decided difference, in the 

 sharp truncation of the postero-dorsal angle, already remarked 

 upon, and whicli in our species is evenly rounded off. L. eichwaldi 

 possesses a marginal flange, but not so well developed as in 

 L. marfjinata, Keys. The figures of L. marginata given with 

 Keyserling's original description shoAv a great variation in size, 

 but the essential characters are the same. Prof. T. Eupert 

 Jones," in reviewing this sjDecies, remarked that he suspected 

 the smaller individual to be an adult form of a distinct species. 

 The present extensive series shows just such a large amount of 

 variation in size, which naturally leads us to conclude that 

 Keyserling's species, like ours, was really subject to great dimen- 

 sional variation. In the relative thickness of the carapace 

 and the position of the central tubercle, the Australian and 

 Petschora-Land specimens agree, leaving the fundamental ;ind 

 characteristic differences of the shape of the hinder end of the 

 carapace as sufficiently striking to warrant a new designation 

 for the Yass examples. 



Other s^Decies of the L. marginata type which may be com- 

 pared with L. sliearshii are L. isochilinoides, Jones, '^ from 

 schistose sandstone of Devonian age. Spitzbergen, and L. 

 nordenskjoe.ldi, Schmidt,"' from Upper Silurian rocks in the 

 Island of Waigatsch. The latter species, however, is not so 

 narrow in front (side aspect), nor so roundly truncate at the 

 dorsal anaie of the hinder end. 



1 " Cytherina balthica," Hisinyer. Lethfea Suecica, 1837, p. 10 and 118, pi. i., fit;s. 2, a, 

 b ; pi. XXX., fig-. 1. 



2 " Ueber die Russischen silurLschen Leperditien." Mem. Acad. Imp. Sei. St. Petersb., 

 ser. 7, vol. xxi., 1874, p. 17, pi.— figs. 19-21. 



3 " Notes on the Palaeozoic Bivalved Entomostraca, Xo. iii. Some species of Leperditia." 

 Ann. Mag. Nat. Hist., ser. 2, vol. xvii., 1856, p. 94. 



4 Ann. Mag. Nat. Hist, ser. 5, vol. xii., 1883, p. 247, pi. ix., figs. 1-9. 



5 Mem. Acad. Imp. Sci. St. Petersb., ser. 7, vol. xxxi., No. 5, 1883, pi. i., figs. 29-32. 



2a 



