496 Udonella Caliebriim 



^' 



a pair of similar legs ; these legs are equal, five-jointed, the 

 two basal joints short, the three outer elongate, tapered, and 

 ciliated along their internal margins with long white hairs : 

 the three segments which follow the large one are short, 

 equal, transverse, bearing each a pair of legs formed for 

 creeping ; these arise within a cup-shaped tubercle, are equal 

 in length, rough, of six joints, and armed with a claw; the joints 

 are emarginate on the superior aspect of their tarsal ends, to 

 allow of freer motion, the femoral is long, the three tibial 

 are short and nearly equal, the first tarsal is twice as long 

 as the second, which bears the claw, under which there is a 

 short spinous projection : abdomen composed of two in- 

 articulate pieces, equal in length to the three preceding, 

 angulated, with a few tubercles, and terminated by a strong 

 triangular spinous process ; on the ventral aspect are two 

 linear-oblong movable plates pointed behind, joining ac- 

 curately in the mesial line, and enclosing three pairs of white 

 branchial processes : each of these consists of a stalk, which 

 supports two equal flattened lamellae, movable, beautifully ci- 

 liated on their sides, and more especially on their truncate 

 apices, with long plumose bristles. 



Astacilla longicornis is apparently not uncommon in Ber- 

 wick Bay; but, as it is a pelagic species, I have not been able 

 to procure living specimens, and observe its mode of pro- 

 gression. The tubular ciliae of the superior antennae are very 

 singular organs, the like of which I do not remember to have 

 observed in any other isopodous crustacean insect. The 

 joints of the inferior antennae are deeply cut on the under 

 sides, so as to allow of their being bent under the body ; but 

 they cannot be carried above its level, or laid on the back, as 

 by the terrestrial species of the order when they are alarmed. 

 The large middle segment serves the purpose of an ovarium, 

 and, at certain seasons, is filled with numerous orange-coloured 

 or reddish globular ova. When these are mature, the seg- 

 ment opens, by a natural rupture, along the medial ventral 

 line, and permits their discharges, in the same manner that 

 the belly of the pipe-fish opens for the escape of its spawn. 



44. Udone'lla Caligo" rum. {fig. 45.) 

 I have given this little leech a new name ; for I can find no 

 established genus to which it can be referred. It is the 

 parasite of the parasitical Caligus, which infests the halibut 

 (Hippoglossus vulgaris), and which, appearing to be non- 

 descript, will probably afford us the subject of a future 

 illustration. The leech adheres by its sucker to any part of 

 the body of the crustacean, and often fringes the sides, or 



