See Hudson in Month. Micr. Journ. vol. vi. 1871, pp. 121, 215, and Quart. Journ. Micr. Sci. (n.s.) xii. 1872, p. 333; Lankester, ibid. p. 338; Levander in Act. Soc. Faun. Fenn. xi. 1894.
In Denk. Ak. Wien, vol. vii. 1854, 2 Abth., p. 15. As has been suggested by Deby and by Daday, it is not impossible that Hexarthra is identical with Pedalion (and in this case the latter name, as newer, should be suppressed in favour of the former); but we must suppose that Schmarda's figure of the front view is a combination, more or less from memory or notes, of two sketches or notes taken some time before publication; the one a side view somewhat obliquely flattened, showing the two eyes as in Levander's Fig. 3; the other a front view, showing the two pairs of lateral limbs in their correct positions under pressure.
The male of Rhinops vitrea is exceptional in possessing a complete, functional alimentary canal, with mastax, stomach, and intestine (Rousselet). That of Proales werneckii has a mastax, but no intestine (Rothert).
For a full account of this group see Claus in Festschr. Z.-B. Ges. Wien, 1876, p. 75; and Plate in Mt. Stat. Neapel, vol. vii. 1886-87, p. 234; Ann. Nat. Hist. ser. 6, vol. ii., 1888, p. 86.
[Eighteen more have since been recorded.]