192 FOURTH REPORT — 1834. 



of the article Crustaceology in the Edinb. Encyclop., a pa- 

 per in the Linn. Trans. *', and the Malacostraca Podophthalma 

 Britannia, this last giving descriptions and coloured represen- 

 tations of a large portion of the British species, have been already 

 alluded to in a former part of this Report. These works were 

 all published before the first edition of ih^ R^gne Animal of Cu- 

 vier. Nevertheless it may be well to give a slight sketch of Dr. 

 Leach's arrangement, which, though founded upon Latreille's f, 

 is somewhat different from that proposed subsequently by this 

 last author. 



In the LinncEan Transactions, ahove referred to. Dr. Leach 

 distributes the Crustacea primarily into the two large groups or 

 subclasses of Malacostraca and Entomostraca. The Malaco- 

 straca are then divided into two other groups, or legions as they 

 are called, bearing the names of Podophthalma and Edrioph- 

 thalma, according as the eyes are either pedunculated or sessile. 

 The Podophthalma include the two orders Brachyiira and 

 Macroura, comprising, the former thirty-three, and the latter 

 twenty-two genera. The Edriophthalma are not di\ided into 

 orders, but merely distributed into thirty-eight genera, which 

 are grouped according to the form of the body, and other cha- 

 racters derived from the antennae and feet. In this division are 

 several new and curious genera, entirely unknown till Dr. Leach 

 first made them public. The Entomostraca had received so 

 little attention when Dr. Leach published his system, that he 

 did not attempt to arrange them according to their true affini- 

 ties, but merely gave an artificial distribution of the genera, to 

 serve till such time as we were made better acquainted with 

 their structure. 



The arrangement of Latreille in the third volume of the first 

 edition of the Rbgne Animal % is different, as already alluded 

 to, from that adopted formerlj'' by this author. In this work 

 the Crustacea are divided into five orders : Decapodes, Stoma- 

 podes, Amphipodes, Isopodes, and Branchipodes ; the charac- 

 ters of which are taken from the situation and form of the 

 branchicc, the mode of articulation of the head with the trunk, 

 and the organs of manducation. The Decapoda are divided into 

 the two families of Brachyiires and Macroiires, answering to 

 Dr. Leach's two orders bearing the same names. The Stoma- 

 poda include one family, formed out of the Fabrician genus 



* vol. xi. p. 306. 



f I allude to the system given by Latreille in his Genera Crustaceorum et 

 Insecforum. 4 vols. 8vo. Paris, 1806. ' 



X Latreille undertook all that portion of the above work which treats of the 

 jinnulose Animals with Articulated Feet, comprising the classes Crustacea, 

 Arachnida, and Insecta. 



