PALiEOCORYSTES. 11 



belonging only to one known recent species, Myra elcgans ;* it is also, with the exception 

 of the slightly projecting frontal and orbital regions, nearly of the form of half an egg, 

 suggesting the generic name which I have given to it. The essential characters are, how- 

 ever, sufficient to establish its true affinities. The uninterrupted smoothness of the surface, 

 the slight projection and truncation of the frontal portion, the small size, position and 

 direction of the orbits, and the form of the oral aperture, all concur in supporting this 

 view of its affinities. 



I have named the species after Mr. Cunnington, of Devizes, whose papers on the 

 geology of Wiltshire are well known, and to whose kindness I am indebted for the loan of 

 the whole of his interesting collection of Crustacea from the upper Greensand of that county. 



Sub-Order— OXYSTOMATA. 

 Family— CORYSTIDJE. 



Genus — Paljeocorystes, Edwards, Bell. 



Char. Gen. Testa longior quam latior, depressa, postice gradatim angustior, margine 

 latero-anteriore dentato, rostro brevi. Orbitce latoe, ovales, mediocres, supra bifissae. 

 Pedipalpi externi caute exteriore lineari, apicem versus angustato ; caulis interioris arti- 

 culo secundo lineari, tertio bis longiore quam latiore. Pedes antici aequales ; posteriores 

 reliquis multo minores. Abdomen in utroque sexu segmentis omnibus separatis, quinque 

 prioribus brevibus, sexto quadrato, septimo semiovali. 



The carapace in all the species of this genus at present known is strikingly similar to 

 that of the recent species Corystes Cassivelaunus, so common on most of our shores. It 

 is considerably longer than it is broad ; the front has a small rostrum ; the orbits are of 

 moderate size, and have two fissures in the upper margin. The oral opening is rather 

 narrow, and extends forwards to near the point of the rostrum, where it terminates in an 

 acute angle, and the epistome is extremely small. The external footjaws are narrow, both 

 the stalks linear, and the external one pointed and slightly curved at the apex. The third 

 joint of the internal stalk is inserted at the middle of the truncated extremity of the 

 second, and is twice as long as it is broad. The legs are more or less robust, excepting 

 the last pair, which are very much smaller than the preceding ones, and placed con- 

 siderably above their level. The abdomen has parallel sides, the first five segments are 

 short, the sixth quadrate, and the seventh semioval, approaching triangular. There are no 

 intercalary pieces at the angles of the junction of the sixth and seventh segments. 



This genus, to which, from an erroneous notion of the structure of the posterior pair of 



* Bell, "Monogr. of the Leucosiadse," • Lin. Trans.,' xxi, p. 297, t. xxxii, fig. 4. 



