92 BRITISH CAMBRIAN TRILOBITES. 



the margin generally appears to be entire (as described by Angelin), but Persson 

 states that in well-preserved specimens the constituent segments project slightly 

 at their terminations, forming small points ; l the axis of the tail shows two 

 distinct rings besides the terminal portion. 



In the width of the axis L. ovatus, Ang., 2 approaches the present species more 

 closely, and, moreover, its thorax bears a row of median tubercles ; but the 

 marginal teeth on the tail are more conspicuous. It may be remarked that in the 

 specimens figured by Holtedahl 3 as L. ovatus, both the glabella and the thoracic 

 axis appear too narrow for Angelin's species. Holtedahl thinks that this may be 

 due to the fact that the axis is really highly convex, as in his specimens, but that 

 in the Swedish specimens, which are preserved in shale, it has been flattened, 

 and consequently widened, by pressure. 



In L. raphidophorus, Aug., the axis bears a row of median tubercles, and in 

 one of the posterior segments the tubercle becomes a spine. This species, 

 however, has not yet been fully described or figured. 



L. broggeri, Holtedahl, 4 is distinguished from L. salteri mainly by the narrower 

 axis and the absence of median spines. The tail has a narrow marginal fold with 

 no trace of spines, and resembles that of L. salteri more closely than the tail of 

 any of the other species. 



L. lotigdspinus, Holtedahl, 5 is too imperfectly known to permit of any useful 

 comparison. 



None of the Scandinavian species appear to possess the row of median spines 

 characteristic of L. salteri. In L. raphidophorus a long spine springs from one of 

 the posterior thoracic segments — according to Angelin from the last but one — but 

 the remaining segments bear simple tubercles. In L. ovatus there are median 

 tubercles but no spines, Avhile in L. stenotus the axial rings are without even 

 tubercles. Nevertheless, considering how many specimens of L. salteri might be 

 examined without discovering any indication of spines, it would be unsafe to 

 assume that the Scandinavian forms bore none. 



Raw has suggested that L. salteri should be taken as the type of a new 

 subgenus, which he calls Leytoplastidss and in which he includes the Acerocare 

 claadicans, A. norvegicum 6 and A. paradoxum of Moberg and Moller. The head 



1 In most of the specimens that I have myself examined the margin seems to be entire, but one or 

 two showed small points. 



2 See Persson, loc. cit., p. 520, pi. ix, figs. 17 — 23. 



3 See Norsk, geol. Tidsskr., vol. ii, no. 2 (1910), pi. i, figs. 4, 6, 7. 



4 Ibid., p. 18, pi. iii, figs. 1—10. 



5 Ibid., p. 11, pi. iii, figs. 12, 13, ? 14. 



6 This is the name applied by Moberg and Moller to the specimen described by Brogger as 

 Cyclognath/U8 microjjygtts, Lnrsn., which they consider to be distinct from that species. I cannot for 

 my own part see any reason for placing it either in Leptojdastns or in Lejptoplastides. The eye is set 

 far forwards and close to the glabella, there are no genal spines, and the form of the free cheeks is 

 similar to that of Peltura and not to that of Leptoplastus. 



