CRUSTACEA FROM THE * CHALLENGER ' EXPEDITION. 55 



Among the living Decapoda Macrura there is hardly a group with which Willemoesia 

 could he said to he very closely allied. Nearest to it are undouhtedly the Scyllarinae ; but 

 these, like ail the genera of the family Palinuridse, 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, he 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, Willemoesia 

 approaches most closely the fossil Eryontidce. If we compare, for example, our figure 

 of W. crucifera (Plate XII. fig. 10) with a figure of Eryon arctiformis, and the description 

 of the " Tribu des Eryons," given hy Milne-Edwards * (and probably taken especially 

 from Desmarest's ' Crustacea Eossiles '), we find most striking resemblances between the 

 two forms. In W. crucifera as well as in JEryon the carapace has nearly half the length of 

 the whole body ; and in both forms its lateral borders are wing-like expansions which 

 are divided by two deep incisions into three portions. The anterior border of the carapace 

 is nearly straight in both forms. 



Eryon was probably not blind ; for the eye-stalks have been found in several specimens. 

 Its antennae seem to be somewhat more reduced than in Willemoesia ; but the second 

 pair of them has, according to Desmarest, " une ecaille assez large, ovoiide et forte- 

 ment echancree." This is the chief difference between Eryon and the Palinuridse, and 

 the same in which also Willemoesia differs from that group. 



Milne-Edwards says nothing on the parts of the mouth ; but according to Quenstedt 

 they had a very large mandibula, one of the teeth of which was preeminently strong. 

 This is very much like what we find in Willemoesia ; but in the fossil genus palpi were 

 present at the base of the first and second gnathopods, which are wanting in the living 

 genus. The first pair of pereiopoda is in both forms longer than the following ones, and 

 terminated by a pair of long and slender chelae. In Eryon three pairs of pereiopoda, in 

 W. leptodactyla five, and in W. crucifera four are terminated by chelae. The form of the 

 last pereiopod in E. arctiformis is exactly the same as in W. crucifera ; and the abdomen 

 of these two forms is, as the above-mentioned figures show, so very much alike in the 

 two forms, that, if the last pair of pereiopoda and the pleon of Dry on were presented to me 

 without my knowing to what they belonged, I should undoubtedly declare them to be 

 parts of the genus Willemoesia. There are the same line of spines at the top of the 

 rings, the same winglike expansions on both sides, and that characteristic " nageoire 

 caudale, dont la lame m£diane est pointue et les quatre lames laterales moins longues 

 que la mediane et hastiformes." Also the fine fringe of hairs which distinguishes the 

 caudal fin of Willemoesia is to be seen in the fossil crustacean. 



Eryon differs from the living genus chiefly by the presence of eye-stalks and of palpi at 

 the base of the gnathopoda. According to Quenstedt the latter were observed only with 

 some difficulty ; and their presence seems not to be beyond all doubt. I shall only on my 

 return be able to look myself over the original specimens and papers, and then, I hope, 

 be able to give a more detailed account on the relations of Willemoesia to Eryon. 



* Histoire Naturelle des Crustacea, tome ii. (Paris, 1837) p. 278. 



