Proof that these are appendages of a Calymene is of course wanting, but there is no particular reason so far to say that they are not.
Measurements: Two of the more complete specimens, each showing six segments, are each 8 mm. long.
Somewhat similar to the specimens from Covington are the ones described by Eichwald (1825, p. 39, 1860, pl. 21), the specimens being from the Silurian of Gotland. The figure copied by Walcott (1881, pl. 6, fig. 4) has never been looked upon as entirely satisfactory evidence of the nature of the specimen, and so far as I know, the fossil has not been seen by any modern investigator.
Ceraurus pleurexanthemus Green.
(pl. [11]; text figs. [12], [17]-[19], [21], [22], [24], [29], [30].)
Illustrated: Walcott, Ann. Lye. Nat. Hist. New York, vol. II, 1875, pl. 11;—31st Ann. Rept. New York State Mus. Nat. Hist, 1879, pl. 1, fig. 3;—Bull. Mus. Comp. Zool., Harvard Coll., vol. 8, 1881, pl. 1, figs. 1-5; pl. 2, figs. 1-4, 6-8; pl. 3, figs. 2, 4-7; pl. 4, figs. 1, 2, 4-6, 8; pl. 6, fig. 3; Smithson. Misc. Coll., vol. 67, 1918, pl. 26, figs. 8, 14, 15; pl. 27, figs. 1-3, 5a, 6-9, 12 (not Calymene), (not 15, Calymene); pl. 28, figs. 1-5; pl. 34, fig. 1; pl. 35, fig. 7.—Milne-Edwards, Ann. Sci. Nat., Zoologie, ser. 6, vol. 12, 1881, pl. 10, figs. 1-18.—Bernard, The Apodidæ, 1892, text figs. 46, 51.
No trace of antennules has yet been found.
I find only three sections cut through the plane of the hypostoma of Ceraurus which show anything of the cephalic appendages, and no one of them is very satisfactory. The best is No. 22, the one figured by Walcott (pl. 3, fig. 2, 1881; pl. 27, fig. 12, 1918), but one should remember that this section is not actually cut in the plane of the hypostoma but is a slice diagonally through the head, cutting through one eye and the posterior end of the hypostoma. It shows what seem to be the coxopodites of the second, third, and fourth pairs of cephalic appendages, the exopodites of the third and fourth pairs, and the metastoma. If this interpretation is correct, the first pair of gnathites lay alongside the hypostoma or under its edge, and were feebly developed, the second pair were attached in front of the tip of the hypostoma, curved back close to it, and their inner ends reached the sides of the metastoma. The third and fourth pairs were back of the metastoma, the third pair was stronger than the second, and the fourth probably like the third.