REPORT ON THE CRUSTACEA MACRURA. 115 



British Museum Collection), as well as in other specimens less distinctly pronounced. In 

 an unnamed specimen (No. 44930) this squamose enlargement exists on the preceding 

 as well as on the penultimate joint, especially on the inner side. In some species it is 

 not present at all, the penultimate joint of the peduncle being subcylindrical, but I have 

 not seen any species among the numerous specimens in the British Museum Collection in 

 which the scaphocerite can authoritatively be pronounced to be present, except in Eryon 

 spedosus (Minister) (No. 44808), where it appears to exist on each side ; but the condition 

 of the specimen is fragmentary. 



The oral appendages, so far as my own observations go, have not been made out ; but 

 Dr. v. Willemoes-Suhm quotes Quenstedt as having stated that Eryon had a very large 

 mandible, one of the teeth of which was preeminently strong, and that the palpi were 

 present at the base of the first and second gnathopoda. They are reduced but not 

 wanting in Pol ycheles and its allies, but are homologous not with the basecphysis but with 

 the mastigobranchia, originating as they do in the coxal joint. No other observer since 

 Quenstedt has seen them in Eryon; we are not, however, justified in excluding his 

 evidence until the specimens from which he obtained his information have been re- 

 examined. The second and third siagnopoda are broad, foliaceous, of extreme tenuity, 

 whereas the basecphyses, judging from what we know of other forms, are more or less 

 long, narrow, and tapering, unless degraded to a rudimentary condition, when they retain 

 a more or less distinctive rod-like character. Quenstedt could scarcely have mistaken 

 them for any other parts, as the Rev. Dr. Norman suggests, if we are to assume any 

 resemblance in their structure to those of other Crustacea. 



The pereiopoda are extremely like those of Polycheles crucifera. The first pair is 

 long, having the carpos short, the fingers of the chela long, slender, and overlapping at 

 their extremities ; the three succeeding pairs are short and chelate, with narrow propodos 

 and slender fingers ; the fifth pan is short, and not chelate, the dactylos being long and 

 styliform. 



One great anatomical distinction between Polycheles and Eryon appears to lie in the 

 character of the ophthalmopoda, which occupy the same position in relation to the antennas 

 in both fossil and recent forms. In the recent genera, with the exception of Eryoneicus, 

 the latero-anterior angle of the earapace is largely developed and overrides and covers a 

 large portion of the peduncle of the eye, leaving only a deeply incised orbit that allows 

 a portion only of the base to become visible on the dorsal surface. Even this is entirely 

 obliterated in Willemoesia. 



In Eryon the increased development of the antennal region of the carapace is 

 wanting, consequently the organ of vision, instead of being covered and hidden from 

 view, is exposed upon a peduncle, which in some species appears to be projected on a 

 prominence. 



If we examine the specimens from the Lias of England, we shall find that the latere- 



