436 Dr. H. Woodward—On the genus Eryon. 
granular. The telson has three longitudinal ridges upon it. The 
tail-lobes or swimmerets are broadly rounded, and the outer plate 
has a dizresis across its lower extremity. The surface of the carapace 
is strongly granulated, the centre or dorsal line being marked by a 
strong line of tubercles which die out forwards, just beyond the 
cervical furrow. In addition to the dorsal ridge two lateral lines of 
smaller tubercles further subdivide the carapace longitudinally, 
marking off the branchial region on either side. The lateral margins 
of the carapace are also marked by minute spines and tubercles. 
Referring again to Mr. C. Spence-Bate’s remarks on the genus 
Eryon, including as at present constituted many species from the 
Solenhofen Limestone in which the dizresis, or suture dividing the 
outer lobe of the caudal fin, is absent, and many from the English 
Lias, ete., in which it is distinctly present, Mr. Spence-Bate contends 
—and he is probably justified in his contention—that the absence or 
presence of this dizresis is of generic, if not of family, value; and 
further that there are many other distinctive characters amongst 
the various species of Eryon which are of sufficient importance to 
constitute generic differences. He has separated from the genus 
Eryon, under the name of Archeastacus Willemesii, a Liassic form 
from Lyme-Regis (see Grou. Maga. 1884, Pl. X. and p. 3807; see 
also “Challenger” volume, 1888, p. 117), which he believed had no 
digresis, but which has in fact a well-marked one. Apart from this, 
it has no salient character which would entitle it to be treated as 
generically distinct from other Liassic forms of Eryon. But if the 
presence or absence of a digresis in the outer lobe of the tail-fan be 
deemed of generic value, then all those forms in which this suture 
is absent, must be retained in the genus Eryon,' whilst those in which 
a digresis is present, must form a new genus. 
Unfortunately the name Archezastacus, proposed by Mr. Spence- 
Bate, cannot stand, as it was given in error to a form which its 
author believed to be destitute of a digresis, whereas it possesses one. 
But if the Liassic species must be separated for this reason from the 
genus Hryon, then Broderip’s genus Coleia (1835) should be revived, 
as having the priority, by more than fifty years, over the generic 
name proposed by Spence-Bate. 
Mr. Spence-Bate quotes the writer as to the rarity with which the 
eyes are found preserved in fossil forms of the genus Hryon. He 
writes: “'The eye is but rarely if ever preserved, and Woodward 
says, ‘has never been positively determined, and the peduncle on 
which it is supposed to stand frequently appears as if it were 
biarticulated ; but I have never seen a specimen, or the figure of 
one, in which the perfectly-formed eye has been found so as clearly 
to determine its form and character.” 
I cannot find the above italicized quotation, but I do say (Quart. 
Journ. Geol. Soc. 1866, p. 496): “The eyes, but rarely preserved, 
are placed ””—in Hryon Barrovensis—‘“ near the base of the scale of 
the outer antenne.” Again under /. Brodiei (op. cit. p. 498): “In 
this specimen, one eye is preserved in siti.” 
1 The genus Evyon was founded by Desmarest on specimens from Solenhofen 
which have xo dieresis in the tail-fan. 
