PAL^OCORYSTES. 13 



The genus, then, as far as regards this country, consists of three species, and the struc- 

 tures which I have found common to them all, and which have been cognizable in the 

 numerous specimens which I have examined, have enabled me to construct the above 

 generic character.* 



I have a few observations to make with reference to the true relations of the genus, 

 which, as I have before stated, appear to me to have been misunderstood. 



Professor M'Coy — after stating that " in the general form of the carapace, of the rostrum, 

 in the completeness and form of the orbits, with the two fissures in their upper edge, it 

 so exactly resembles Corystes as to have even deceived Dr. Leach, the first crustaceologist 

 of his day" — with the greatest confidence refers the genus to the order Anomura, on the 

 single ground of the abruptly smaller size of the last pair of legs, and their being placed 

 on a higher level than the others ; whilst he acknowledges that he had not had an oppor- 

 tunity of ascertaining whether there are any supplementary pieces between the sixth and 

 seventh segments of the abdomen, which is by far the more important character. In fact, 

 the small size of the hinder pair of legs, and their elevated position, is a peculiarity which 

 occurs in many other forms of undoubted Brachyura. In the whole family of the Dorip- 

 pidse, for example, it is as strongly marked as in any of the Anomura; and in the typical 

 recent species of the present family, Corystes Cassivelaunus, this pair of legs is on nearly 

 as high a level, with relation to the preceding ones, as in either of the fossil species. A 

 specimen in the collection of Dr. Bowerbank, in which several joints of the posterior pair 

 of legs exist, shows distinctly that they are not turned over the back at all. Whilst, there- 

 fore, I am thus enabled to place the genus in its true relation, I am at the same time 

 compelled to change the name given to it by Professor M'Coy under a mistaken impression 

 as to the structure of these feet. The non-existence in the present species of the inter- 

 calary pieces in the abdomen, which are so conspicuous in all the Dromiadse; including 

 the extinct genus Dromiolites, described in the former part of this monograph, forms an 

 additional proof, in the absence of all other anomurous characters, that Leach was not 

 " deceived " when he referred the genus to the family Corystidse, a view which is confirmed 

 by the structure of the external footjaws and the form of the oral opening. 



It is remarkable that the species of this genus are very subject to be infested by a 

 parasite, probably nearly allied. to Bopyrus, which occasions a large swelling on the branchial 

 region, and doubtless occupied the branchial cavity. This is precisely the situation in 

 which Bopyrus is found in several recent species of the Palsernonidse and their allies, but I 



* Two species of this genus have been found on the Continent, both of which are specifically 

 distinct from the British ones. One of these, Notopocorystes Mulleri of Count von Binkhorst, considerably 

 resembles Palceocorystes Broderipii, and is from the Maestricht beds. The second is P. Frigeri of 

 Professor Milne Edwards, which has many characters in common with that species, but is undoubtedly 

 distinct. Eumorjihoeorystes sculptus of the former author has the peculiar sculpture on the carapace which 

 distinguishes Eucorystes Carteri, but in the former the sculpture extends over the whole carapace, whilst 

 in the latter it is confined to the anterior half. 



