Dr. H. Woodward — A Neiv GauU Crustacean. 63 



mark each lateral margin, the hindmost and most prominent pair 

 being situated on a transverse V-shaped ridge and furrow, which 

 cuts off the posterior fifth of the carapace, and meeting in the centre, 

 where it is marked by the single median posterior tubercle already 

 referred to.^ The three succeeding pairs of marginal tubercles are 

 about equal in size, and the front pair forms the outer angle of the 

 orbital fossa. The rostrum is subdivided or notched in the centre, 

 having a A-shaped groove running down it, the base of which is 

 directed forwards, and the diverging points reaching to the first pair 

 of sub-central tubercles which mark the gastric region. The orbits 

 are large and well defined. No nuchal furrow is visible. The 

 carapace is not in the least crushed or distorted, and the surface 

 is well preserved. 



Differences and Affinities. — A careful comparison of our Brachyuran 

 with the various species from the Gault and Greensand affords but 

 little assistance in the specific determination of the specimen. In 

 Necrocarcinus, when the rostrum is preserved it is not notched or 

 bifurcated, but pointed in the centre ; the median line of the 

 carapace is not simple, but divided into distinct gastric and cardiac 

 regions, and an anterior nuchal furi'ow can be traced ; the carapace 

 .8 broader than long; the marginal tubercles are not prominent, and 

 the posterior or metabraTichial furrow is absent. 



Turning to Dromilites from the London Clay, one is at once struck 

 by many points of resemblance. The carapace (as in our Gault 

 fossil) is longer than broad, is very tuaiid, the rostrum is bifurcated, 

 there is a median furrow, the tubercles are arranged in pairs ; four 

 pairs of marginal tubercles are present, the posterior metabranchial 

 furrow is also seen ; the orbits are large and conspicuous. 



Unfortunately the other ventral aspect of the carapace is wanting 

 in the Gault fossil. 



Prof. Bell (" Fossil Malacostracous Crustacea of Great Britain," 

 Mon. Pal. Soc. : Part ii, ' Crustacea of the Gault and Greensand,' 

 1862, p. v) remarks : — " The Crustacea of the strata below the Chalk 

 present several remarkable peculiarities in their forms 

 and affinities. One of the most interesting of these is the existence 

 of analogous or, so to speak, representative species in these beds and 

 in the London Clay " (see part i of same Mon., ' Crustacea of the 

 London Clay,' op. cit., 1857, pis. v and vi). "In some cases this 

 representation is shown in their specific distinction, with the most 

 perfect generic identity, as in the case of Hoploparia, of which we 

 have already seen two very distinct species in the later formation, 

 and we have now described no fewer than six species in the earlier 

 deposits. In no instance do any of these locally separated individuals 

 belong respectively to the same species ; in every one the specific 

 distinctness is unambiguous, but the generic relation to each other 

 is no less so. Another case of nearly similar import occurs in the 

 anomourous family Dromiadae ; the Homolopsis of the Greensand 



' This line may be defined as the ' metabranchial furrow,' and is seen in 

 Plagiophthalmus ovi/ormis from the Greensand of "Wilts, and in Dromilites from 

 the London Clay. 



