200 FOURTH REPORT — 1834. 



respond with those noticed in Branchipus, Apus, and other 

 genera of the Phi/Uopoda, to which the Artemis is allied. Mr. 

 Thompson has endeavoured to prove that there is a close affinity 

 ht\.v<&en the Artemis salinus and the fossil Eyeless Trilobites. 



I may also refer to a paper by Audouin and Edwards in the 

 Annates des Scien. for 1826*, containing an account of a very 

 singularly organized animal, forming a new genus {Nicothoe) 

 among the Siphonostoma of Latreille. It is of parasitic habits, 

 and was discovered firmly attached to the gills of the Lobster. 

 Perhaps there is no group in the Entomostraca in which we 

 may expect so many new forms yet to occur, and of whose 

 oeconomy in general we know so little, as that just mentioned. 

 With reference to this last point we may, however, except the 

 genus Argidus, Jurine's memoir before spoken of leaving us 

 scarcely anything further to be desired in the history of that 

 animal. 



3. Arachnidu. — This class, which Lamarck was the first to 

 separate from that of Insects, has until very recently been much 

 neglected by naturalists. The consequence is that our know- 

 ledge of many of the groups contained in it is extremely imper- 

 fect. Even its limits are far from being determined ; and some 

 are of opinion that it ought to be resolved into two classes, on 

 account of the great difl"erences which occur in the respiratory 

 organs. Dr. Leach was the first to entertain this last idea, in 

 the third volume of his Zoological JMiscellam/, published in 

 181 7. In an article in this workf " On the Characters of the 

 Arach/tides," he has restricted this class to the five families 

 of Scorpionidce, Tarantididie, Phalangidce, Solpugidce, and 

 Araneidce, in all of which respiration is effected by means of 

 pulmonar)- sacs. The Trachean Arachnida of Latreille, except- 

 ing the genera Pycnogonum, Phoxichilus, Ammothea, and 

 JS'^ymp/iKm, (whose situation he considers doubtful,) and the 

 genera. P/ialangium,So/puga, and Trogulus, (and perhaps Siro,) 

 he thinks constitute a peculiar class, which he proposes to name 

 Acari. 



Although Lati'eille himself subsequently adopted this same 

 opinion respecting the propriety of forming two classes of the 

 Pulmonary and Trachean ArachnidaX, he has not acted upon it in 

 any of his published works. In the Regne Animal these groups 

 simply stand as two orders, the first including the two families 

 of Filenses {Aranea, Linn.) and Pedipalpes {Tarantula, Fab., 

 and Scorpio, Linn.), the second those of Faux Scorpions, Pyc- 



• torn. ix. p. 345. \ p. 46. 



X Fam. Nat., p. 317, note ('). Coins d'Entom., p. 161. 



