122 DEVONIAN FAUNA. 
2. PfNnTAMERUS BIPLICATUS, Schnur. Pl. XIV, figs. 4, 4a, 5. 
21843. TErEBRaTULA WurmMul, F. A. Romer. Verst. Harzgeb., p. 19, pl. v, fig. 15. 
1854, PENTAMERUS BIPLICATUS, Schnur. Paleontographica, vol iii, p. 196, pl. 
xxxi, figs. 3a, b. 
1854. — ForMosus, Schnur. Ibid., p. 197, pl. xxxi, figs. 2 a, b. 
1854. on ACUTOLOBATUS, Sandberger. Verst. Rhein. Nassau, p. 345, 
pl. xxu, fig. 15. 
1865. — BIPLICATUS, Davidson. Brit. Foss. Brach., vol. iii, pt. 6, p. 
73, pl. xiv, figs. 31, 32. 
1867. — — Trenkner. Paleont. Novit., pt. 1, p. 18, pl. ii, 
figs. 88 a—e. 
1867. oe acuroLoBatus, Trenkner. Ibid., p. 19, pl. ui, figs. 87 a—e. 
1868. — GALEATUS, Dames. Zeitsch. Deutsch. Geol. Gesell., vol. xx, 
p- 498. 
1882. — BIPLICATUS, Davidson. Brit. Foss. Brach., vol. v, pt. 1, p. 42, 
pl. ii, fig. 22. 
1885. _ — Maurer. Abhandl. Grossh. MHessisch. Geol. 
Landes., vol. i, pt. 2, p. 215, pl. ix, 
figs. 4—4 b. 
1885. —_ ACUTOLOBATUS, Maurer. Ibid., p. 216, pl. ix, figs. 5—6. 
1889. —— GALEATUS, Toll. Mém. Acad. Sci. St. Pétersbourg., ser. 7, vol. 
xxxvil, No. 3, p. 24, pl. u, figs. 16 a, 6, d, e. 
1891. — — Whiteaves. Contrib. Canad. Palzont., vol. i, pt. 3, 
p- 234, pl. xxx, fig. 2. 
Localities.—There are about twenty examples in my Collection and one in the 
Woodwardian Museum from Lummaton ; three others in the Torquay Museum, pro- 
bably from the same locality ; and one from Barton in the British Museum, which 
was figured by Davidson. In Mr. Vicary’s Collection is a rather large specimen 
from Wolborough, and another is in the Museum of Practical Geology. 
Remarks.—Davidson had only small specimens when he first recorded this 
species. Since then larger examples have come to light, one of which he figured 
in his Supplement. The series now before me seems to give a good idea of the 
limits of the species. When young there is little more than a shallow rounded 
fold, slightly hollowed in the centre, on the ventral valve, and a corresponding 
sinus in the dorsal valve, which is prolonged into a kind of tongue. As the shell 
increases in size the central fold becomes more definitely bifid, and one or two 
ribs make their appearance on the lateral parts. When the shell is full grown 
these divisions have developed into steep rounded ribs, so that the margins meet 
in a deep zigzag, the central tongue of the sinus being more or less deeply 
indented. In this stage the shell appears exactly to agree with P. formosus, Schnur, 
