112 THE VOYAGE OF H.M.S CHALLENGER. 



The figure of the fossil specimen demonstrates that the form of the pereionic append- 

 ages bears a strong generic resemblance to Synaxes. I have not had an opportunity of 

 examining any specimens, and gain my impressions of this genus from the published 

 engravings. The first pair of antennae has evidently been forced below the second pair, 

 which is reduced in length and enlarged in diameter; the flagcllum being short, broad, and 

 multiarticulate, is suggestive of a gradual approximation to the form as it exists in the 

 Scyllaridae. The structure of the animal has yet, however, to be more thoroughly examined 

 in detail before its true relation to recent Crustacea can be satisfactorily pronounced. In 

 some of the earlier figures of Polycheles, the animal was represented as being blind and 

 having a laterally compressed rostrum, but the eyes have since been demonstrated, and 

 the supposed rostrum has been shown to be the result of inner margins of the first pair 

 of antennae being extended and forced upwards by lateral compression, and thus 

 .simulating the form of a narrow rostrum. Dr. Camil Heller, who has the privilege of 

 being the earliest observer who described and figured Polycheles, 1 considers that in the 

 general form of the body it " bears a strong resemblance to the Scyllaridae, from which 

 it differs essentially in the structure of the antennae and the form of the chelae ; and 

 corresponds with the Astacidae only in the common possession of the " leaf-like appendage 

 (scaphocerite) at the base of the second antennae, and in the chelate character of the 

 pereiopoda, but differs in all other respects." 



Polycheles, he further says, " corresponds closely with the fossil Crustacean described 

 by Desmarest, from the slate quarries of Solenhofen (Eryon cuvieri), since also in this are 

 found a flattened carapace, and similarly-formed antennae and pereiopoda. The hinder 

 part of the body is much narrower than the anterior ; and the leaf-like appendages " 

 (scaphocerite) " of the second pair of antennae are much enlarged. It forms a link 

 between the Scyllaridae on the one side and the Astacidae on the other." 



Dr. v. Willemoes-Suhm 2 says : — "Among the living Decapoda Macrura there is hardly 

 a group with which Willemcesia could be said to be very closely allied. Nearest to it are 

 undoubtedly the Scyllarinae ; but these, like all the genera of the family Palinuridae, 

 differ from it in the absence of the lamellar appendage of the second antennae, and in the 

 presence of palpi at the base of the gnathopoda, which, as we have seen, are wanting in 

 this new genus. Nor can it, for this latter reason, be referred to the Astacidae, with 

 which it has in common the presence of the antennal scale." 



" It is very astonishing, indeed, that among all crustaceans known to us, Wille- 

 mcesia approaches most closely the fossil Eyrontidw. If we compare, for example, 

 our figure of W. [Polycheles] crucifera 3 with a figure of Eryon arctiformis, and the 

 description " Tribu des Eryons," given by Milne-Edwards 4 (and probably taken especially 

 from Dcsmarest's ' Crustaces Fossiles '), we find most striking resemblances between the 



1 Crustaceen Jes sudlicken Europa, 1863, p. 209, pi. vii. fig. 1. 2 Trans. Linn. Soc. Lond., vol. i. p. 55, 1875. 



3 Trans. Linn. Soc. Lond. vol. i. pi. xii. fig. 10. * Hist. Nat. des Crust., tome ii. p. 278, Paris. 1837. 



