MARINE ISOPODA OF NEW ENGLAND, ETC. 363 



its inferior surface for the delicate pleopods, wliicli arc protected by the 

 operculiform iiropods. Both rami of the uropods are present in our 

 species, but the outer is much tlie larger and conceals the delicate inner 

 ramus in an exterior view. The outer ramus only is thickened and of 

 fuuctional importance as an operculum. 



The habits of these animals are described by Goodsir in the Edinburgh 

 New Philosophical Journal, vol. xxxi, i). 311. He says, "With the 

 dredge I have procured specimens * * * * alive, and have kept them 

 in glass jars of sea- water with sand and corallines, and have thus been 

 enaljled to watch their habits closely. 



" Under the circumstances just stated, each individual will select a 

 branch of coralline, will keep that branch exclusively to itself, and will 

 defend it with the greatest vigor against all intruders. It fixes itself to 

 its resting-place by means of its true thoracic feet, and seldom uses these 

 for progression. When it falls to the bottom of the vessel, it fixes its 

 long pointed antennsB firmly into the sand, and, with the assistance of the 

 true feet, drags and pushes itself forward. This, however, may not be 

 a natural mode of jDrogression, but may be adopted in consequence of 

 the artificial circumstances in which the animal is placed. 



" Swimming is the natural mode of progression. It is amusing to see 

 one of these animals resting, in an erect posture, on a branch of coralline, 

 by means of its true thoracic feet, waving its body backwards and for- 

 wards, throwing about its long inferior antennae, and ever and anon 

 drawing them through its anterior fringed feet, for the pur])ose of clean- 

 ing them. It frequently darts from its branch, with the rapidity of 

 lightning, to seize with its long antennae some minute crustaceous ani- 

 mal, and returns to its resting-place to devour its prey at pleasure. 



'' In this manner the antennae are the only organs employed in seiz- 

 ing and enclosing the prey, which they drag to the anterior thoracic 

 feet, which hold it while it is being devoured." 



I have discarded Johnston's name Leachia, or according to his orthog- 

 raphy Leacia, proposed in 1825, as being preoccupied by Lesueur,* in the 

 Mollusca in 1821. Astacilla is used by Fleming in the 7th edition of the 

 Encyclopaedia Britannica ; 1842 is given as the date in the copy of the 

 seventh volume of the Encyclopaedia that I have seen, but Johnston re- 

 fers to Fleming in 1835 as authority for the name, quoting the Encyclo- 

 paedia. Fleming says in the Encyclopaedia (vol. vii, p. 502) : "■ The ge- 

 nus was instituted by the Eev. Charles Cordiner of Banff in 1784 for the 

 reception of a British species which has been denominated Astacilla Ion- 

 gieornis.''^ I have not been able to find whether Cordiner published the 

 name at that early date or whether it was a manuscrii^t name only. K 

 actually published in 1784 it would have many years' priority over 

 Arcturus, and the author who would unite the genera should use the 

 name Astacilla. Even if not published until 1835 it appears to have the 

 best claim to recognition as the generic name of the type here treated of. 



*Jour. Acad. Nat. Sci. Phila., toI. ii, p. 89, 1821. 



