ii INTRODUCTION. 



Kossiles,' in which he was associated with Alex. Brongniart. It is unnecessary now 

 to enter into any detailed correction of this system, which, although possessing great merit 

 as containing the groundwork of a sound nomenclature and many valuable suggestions, 

 is still in some respects erroneous and overladen with terms which are too circumscribed, 

 and in some instances referred to organs with which they have no very obvious relation. 



Professor Milne Edwards, in his great work, the ' Histoire Naturelle des Crustaces,' 

 improved upon Desmarest's division of the carapace, but it still wanted that simplicity 

 and generalization which are so important in all systems of nomenclature. Dana, Avhose 

 knowledge of the subject and enlarged general views entitle his opinions to great respect, 

 proposed a plan of the regions of the carapace, founded only on their position on the 

 carapace and in relation to each other ; but it appears to me that the memory is greatly 

 aided and the true relation of the regions more nearly approached, by assigning to each 

 its appropriate function, so to speak, as the protecting covering of the subjacent viscus. 

 Still keeping this principle in view, Dr. Milne Edwards has, in a more recent work, 

 his admirable treatise on the homologies of the organs of Crustacea, presented a less 

 complicated nomenclature, which, with some modifications, I shall adopt in the descriptions 

 of genera and species in the present work. 



In following the classification of these parts, as given by this distinguished naturalist, 

 I cannot, however, conceal from myself that there are some points on which, as it appears 

 to me, he is in error. The hepatic region, for example, is one of the smallest of the whole, 

 although the organ to which it nominally stands in relation is of enormous development 

 in the whole of the sub-class with which we have to do, and the region to which the name 

 is given is, by its position, related to only a very small fragment of it. The divisions of the 

 branchial region may, I think, be improved by apportioning a much smaller area to what 

 the author calls the rneso-branchial lobe, a limit which is, in very many cases, indicated by 

 a natural line of demarcation. This alteration I propose to adopt. I should have 

 been disposed to change the names of these, and, perhaps, of some other subdivisions 

 of the carapace, but from a disinclination to interfere with a nomenclature already 

 established by so sound an authority, and thus to create confusion by the multiplication 

 of synonyms in terminology. 



This is not the place to discuss the theory of the homologies of the two primary 

 divisions of the carapace. Much yet remains to be done in this intricate question, and it 

 has recently undergone the investigation of a very competent observer, Mr. Huxley, 

 who has taken the only sure basis for a satisfactory conclusion, that founded upon 

 development. The division, however, into two distinct elements, limited theoretically, 

 and, in many forms, actually, by a definite line of demarcation, is so entirely borne out by 

 facts, that I shall assume it as proved, and found my descriptions upon that principle. 

 This division is most obvious in the Macrura, and some of the Anomura ; but it is by no 

 means rare in the Brachyura, although in these the boundary furrow is less distinguished 

 from the subordinate regional grooves. The sulcus by which it is indicated is termed 



