116 THE VOYAGE OF H.M.S. CHALLENGER. 



frontal angle of the carapace is produced anteriorly to a considerable extent in some 

 specimens, as for instance in Eryon brodei (Woodward), Eryon wilmcotensis (Wood- 

 ward), and Eryon barrovensis (M'Coy), and in others, as Eryon crassicheles and Eryon 

 moorei (Woodward) it is less so. Consequently, in those specimens in which the lateral 

 angle is more developed, a depression corresponding to the orbit or orbital notch in 

 Polycheles is present. Another feature in the British fossil specimens that distinguishes 

 them from those of the Bavarian lithographic limestone, is the presence (according to 

 Woodward) of a well-defined diaeresis or line of division in the outer plate of the 

 rhipidura. 



This feature is common in Astacus and allied genera, but is not present in Poly- 

 cheles, nor any of its congeners. Nor is it to be found in any of the Scyllaridse or Pali- 

 nuridse. Among the Eryons I am only aware of its having been found in one species, 

 and that is Eryon barrovensis, as restored by Mr. Woodward. 



The eye is but rarely if ever preserved, and Woodward says " has never been posi- 

 tively 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. In Eryon brodei the preserved orbit is moderately deep and the latero- 

 anterior angle well advanced. It is the same, but rather less marked, in Eryon 

 wilmcotensis, but in Eryon moorei and Eryon crassicheles, both orbital notch 

 and antennal angle are reduced to a minimum value. All these are from the Lower 

 Liassic rocks of England, except Eryon moorei, which is from the Upper White Lias 

 of Ilminster. 



The several species of Eryon appear to be distinguishable into separate genera, 

 which are as definable from one another as they are distinct from the recent Poly- 

 cheles, but the variability appears not to be greater in those that are separated in time 

 through geological aeons, than in those that are contemporaneous in geographical 

 distribution. 



While studying the fossil forms of the Eryonidse in comparison with those recently 

 brought to our knowledge through the deep-sea explorations, I have found in the collec- 

 tion of Mr. J. Edw. Lee of Torquay a specimen from the Lias of Lyme Regis, that appears 

 to connect the two more intimately than has been shown in the comparison made with 

 any previously known fossil specimen. 



The specimen is fragde and imperfect. One half of the dorsal surface is tolerably 

 well preserved, while the other exhibits only the impression of the form in the matrix. 

 The two conditions are shown in the accompanying figure by a difference in the degree 

 of shading, the darker being that of the external texture, the lighter where the impres- 

 sion of the form is alone retained, whereas the merely outlined portions exhibit the 

 restoration of structure in conformation with known parts. 



