368 Prof. Allman on Chelura terebrans. 



When removed from the water and placed upon a resisting 

 surface, the little crustacean bends the abdomen under the thorax, 

 brings the terminal appendages between the antennse, and then 

 suddenly resuming its straight condition, springs to a consider- 

 able distance. 



The habits of Chelura terebrans are truly xylophagous, and it 

 excavates the timber not merely for the purpose of concealment, 

 but with the object of employing it as food, which is apparent 

 from the fact that the alimentary canal may be found on dis- 

 section filled with minutely comminuted ligneous matter. It 

 will freely attack a piece of timber placed with it in a glass of 

 sea-water, so that its habits may be studied in confinement. 

 Timber which has been subjected to the ravages of Chelura pre- 

 sents a somewhat different appearance from that which has been 

 attacked by Limnoria terebrans. In the latter we find narrow 

 cylindrical burrows running deep into the interior, while the ex- 

 cavations of Chelura are considerably larger and more oblique 

 in their direction, so that the surface of the timber thus under- 

 mined by these destructive animals is rapidly washed away by 

 the action of the sea, and the excavations are exposed in the 

 greater part of their extent, the wood appearing ploughed up, so 

 to speak, rather than burrowed into. Upon the whole, Chelura 

 would seem to be a still more destructive creature than even 

 Limnoria, 



General Considerations. 



Milne Edwards * divides the Amphipoda into two great fami- 

 lies, of which Gammarus and Hyperia may be taken as the re- 

 spective types, assuming as the essential characters of his division, 

 the different conditions presented by the maxillary feet, these 

 differences being found to be for the most part in connection with 

 certain other peculiarities of structure as well as of habits. 



Of the two families thus formed, that of the Gammaridce (fa- 

 mille des Creveitines, Edw.) will include the subject of the pre- 

 sent notice, provided we implicitly yield to the characters drawn 

 from the condition of the maxillary feet. The division however 

 adopted by the great French carcinologist, though adapted to the 

 state of our knowledge of the Amphipoda previously to the dis- 

 covery of the present animal, and separating the then known 

 forms into two sufficiently natural groups, cannot we think be 

 now undeviatingly adhered to, as would seem evident from an 

 attentive consideration of the characters just given of Chelura 

 terebrans. This crustacean has its maxillary feet entirely refer- 

 able to the form of these organs in Gammarus and its allies, and 



* Hist. Nat. des Crust, t. iii. 



