HELMINTIIOCHITON. 
335 
deeply concave in front, in being slightly concave in the latero-posterior part, in 
having very strong apophyses, and in bearing a strong concentric ornament. 
Chiton priscus, Mimster,^ from the Carboniferous, is a much shorter and more 
quadrate form. 
Under the name of Chiton Isevigatas, F. A. Romer, Clarke^ unites the shells 
described by F. A. Romer as Bellerophon expansus^ and Chiton lasvigatus* together 
with Chiton sella, Trenkner,^ This species differs from the English shell in the 
shape of the wing, the concave postero-lateral border, the flattened back, and the 
concentric ornament. 
Chiton trapezoidalis, Trenkner,*' and Chiton gibhosus, Trenkner,'' are very much 
wider and differently shaped forms, while the other species figured by Trenkner and 
reproduced by Clarke are established only on terminal valves, and therefore cannot 
be compared with the present fossils. 
None of the Chitons figured by de Koninck at all approach it. The nearest 
are Helminthochiton gemmatus, de Koninck,^ which is wider, flatter, and more 
recurved along the back, and has smaller wings; and H. miicronatus, de Koninck,^ 
in which the posterior side is larger and the wings very much smaller. 
1 1839, Muuster, ' Beiti-.,' pt. 1, p. 60, pi. xiii, figs. 4 «— e. 
2 ISSi, Clarke, ' Neues Jahrb. f. Miu.,' Beil.-Band iii, p. 337. 
3 1843, F. A. Eomer, ' Verst. Harzgeb.,' p. 32, pi. ix, figs. 5 a, b. 
* 1855, F. A. Eomer, ' Beitr.,' pt. 3, p. 36, pi. vii, fig. 8. 
5 1867, Trenkner, ' Palaont. Novit..' pt. 1, p. 14, pi. ii, fig. 27. 
« Ibid., p. 15, pi. ii, fig. 32, and 1884, Clarke, ' Neues Jahrb. f. Min.,' Beil.-Band iii, p. 338, 
pi. iv, fig. 20. 
7 1867, Trenkner, ' Palaont. Novit.,' pt. 1, p. 16, pi. ii, fig. 33, and 1884, Clarke ' Neues Jahrb. 
f. Miu.,' Beil.-Band iii, p. 339, pi. iv, figs. 12 and 13. 
« 1883, de Koninck, ' Ami. Mus. Kojal H. N. Belg.,' vol. viii, pt. 4, p. 206, pi. li, figs. 28—31. 
Ibid., p. 204, pi. li, figs. 32—35. 
