26 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [XoV. 20, 



examine and study the additions made to the Crustacea from this 

 rich locality, and I now beg leave to submit my further notes Upon 

 them to the Society. 



On the first form (named by me, in my former paper, Palceocorystes 

 glabra) I have no additional materials to present ; but of the genus 

 Rhachiosoma (represented at first by only two imperfectly preserved 

 specimens, named respectively R. bispinosa, and R. echinata) there 

 are now nine examples known. 



The accession of these very perfect specimens, necessitates the re- 

 description of R. bispinosa, for which there are now ample materials. 



Four other specimens, representing two new Eocene forms, about 

 to be described, and a large TJienops, near to T. scyllariformis, com- 

 plete the series. 



Khachiosoma bispinosa, H. "VVoodw., 1870, Quart. Journ. Geol. Soc* 

 1871, vol. xxvii. pi. iv. fig. 3, p. 91. PI. I. 



Although originally supposed to be the smaller form, the discovery 

 of several new specimens of this species shows it to have been fully 

 as large as, or perhaps even larger than, R. echinata. It also proves 

 that the remarkable development of the two lateral spines is a very 

 persistent character in all the individuals ; none of the new examples 

 show a tendency to a branched lateral spine, like that seen in R. 

 echinata, in which the spine appears also to be somewhat flattened, 

 whereas in R. bispinosa it is nearly, if not quite, round in section. 

 These spines have been erroneously spoken of in my former description 

 as "hepatic;" they should more correctly have been styled " bran- 

 chial " or " epibranchial " spines. 



If we compare the figure of R. bispinosa accompanying the earlier 

 description with those now presented (see PL I.), it will be seen that 

 we are now made acquainted, not only with all the limbs (then only 

 known from a single chela in R. echinata), but also with the frontal 

 border of the carapace (so very important and characteristic a part), 

 and with the underside (not visible in either of the first-found ex- 

 amples), revealing the abdomen of both the male and female, and the 

 maxillipeds. 



The hepatic border is armed with three prominent nearly equi- 

 distant spines, whilst a fourth forms the outer boundary of the orbital 

 fossa. The frontal region displays a slight median depression, which 

 may be traced as far back as to the centre of the gastric region, and 

 is marked by a cleft in the rostrum, which thus presents three small, 

 nearly equal serrations on either side, descending towards and form- 

 ing the inner margin of the orbit. 



The superior orbital border is marked by two equidistant fissures — 

 a character, however, which is observable also in the Oanceridce and 

 Oorysticlce, as well as in Portunidce, to which our genus Rhachiosoma 

 undoubtedly belongs. 



The marginal spines on the latero-anterior or hepatic border give 

 to the front of the carapace a slightly sinuous or wavy surface, as do 

 also the two great epibranchial spines, whilst the three tubercles, 

 arranged in a line on either branchial region, contribute by their 



