Invertebrata. Zoological Collections. 177 



and which they designate under the name compound bristles. Two different 

 parts always enter into their composition, which is an essential character. 

 Most commonly the two parts, one basilar, the other terminal, are united 

 end to end by a true ginglymoid articulation, and the terminal portion pre- 

 sents different forms, which may be compared to a hooked knife, harpoon, 

 or bayonet. But the most curious thing connected with these compound 

 bristles is, that the animal can leave the last joint in the wound which they 

 have made, and that the weapon, thus reduced to a basilar portion, still 

 preserves at its extremity a sharp point, which it can use as a stiletto. 



Lastly, the authors have described a kind of arms, of very complicated 

 structure. These are of the form of barbed arrows, the more remarkable, 

 that each carries with it its quiver, or case. This case, composed of two 

 valves, capable of falling down when the arrow is struck into any foreign 

 body, presents internally as many compartments as there are little teeth on 

 the sides of the arrow, and not only contributes to preserve the weapon, but 

 permits its entering into the body of the animal without making any rent. 

 — (Cuvier, Rapport) — Ann. des Sci. Nat. Nov. 1830. 



Notice of the Ropan of Adanson; with other Observations on the MoUusca, 

 By M. Rang. 



M. Rang, who has recently returned from a voyage to Senegal, has 

 addressed a letter to Baron Ferrussac, in which he communicates some of 

 the results of his voyage. 



He has found that the Ropan of Adanson is nothing else than the Modiola 

 caudigera of Lamarck, which envelops itself in a calcareous tube, with which 

 it lines the cavity it has previously hollowed in stone. Lamarck had already 

 seemed to believe in the presence of a tube in the Lilhodomus ; and the 

 discovery of the fact in the living animal is the more important, that 

 M. Ch. Desmoulins has determined it in fossil individuals from the 

 neighbourhood of Bordeaux. 



M. Rang has not been able to find the Sormetus of Adanson : he hesitates 

 in admitting the existence of this molluscum. 



He has found in the Senegal, beautiful Etherics, at a distance of 600 miles 

 from its mouth. 



He has examined the animals of the Corbula, the Ungulina, and also that 

 of the Discina, which, he says, differs little from the Orbicula. 



He has discovered in some rivers the Galathea radiata, which Lamarck 

 quotes as coming from Ceylon. This beautiful shell is found on sand 

 banks, which are covered by some feet of fresh water : with it live eight or 

 ten species of Melanim of exceeding beauty, and which, in form, variety, and 

 size, approach the genus Potamides of M. Brongniart, as well as the fossil 

 CerithicB from the neighbourhood of Paris Ibid. 



Classification of the Arachnides In a detailed anatomical monograph on 



the organs of motion of the bird-catching mygale, (Mi/gale avicularia, Lat.) 

 M. Strauss makes the arachnides an independent class, and places them 

 between the insects and the Crustacea ; he divides them into three orders : — 



1. Pulmonata, in which the air enters a kind of vascular sac, to act on 

 the fluids contained in the vessels. 



2. Tracheaia, which have a respiration analogous to that of insects. 



3. Branchifera, or Gnathopoda, whose feet serve for jaws, and for 

 branchiae, with aquatic respiration. — Cuvier, Rapport. 



VOL. III. 



