CRUSTACEANS 



specimens which, by reason of their smaller size and much more strongly 

 granulated head and body, may be distinct from the common form, 

 but whether for these the name O. fossor, Koch, should be adopted 

 remains uncertain. In the second set the genus Porcellio is as usual 

 represented by the large and very abundant P. sca&er, Latreille, sent by 

 the ladies of Lane End, and reported from Mr. Webb's series of localities, 

 'near Dropmore' being in this case substituted for Hedsor. This species 

 is not quite so broad as Oniscus asellus, and its surface is strongly granular. 

 It is most often of a uniformly blackish grey colour in a general view, 

 though on closer inspection lighter markings can be perceived and the 

 borders are more or less pellucid. Sometimes it is marbled with grey and 

 yellow, and this variety has been distinguished as marmoratus by Brandt 

 and Ratzeburg. In the ordinary form the flagellum of the second antenna? 

 has the two joints nearly equal, or the first a little shorter than the second. 

 In some rather small prettily-marbled specimens submitted by Mr. Webb 

 the first joint is much shorter than the second, a character shared by 

 P. ratzeburgii^ Brandt, from which however in some other respects they 

 differ. At Eton Mr. Webb has met with P. dilatatus, Brandt. This 

 broad, moderately granular species has the two joints of the antennary 

 flagellum short and equal. From the preceding species it is well distin- 

 guished by the apical segment, which, instead of being acutely triangular 

 and dorsally grooved, is flat above and drawn out narrowly tongue-like 

 to a rounded tip. In addition to the above a very handsome species, not 

 hitherto included in the British fauna, has been sent me by the Misses 

 Johnson from Lane End and from Eton by Mr. Webb. This new acqui- 

 sition is P. rathkei, Brandt. It is more or less marbled over all the back, 

 but has also three well-marked longitudinal stripes of pale flecks, which 

 are drawn closer together on the pleon than on the person. The surface 

 is moderately granular, but the hind margins of the person segments are 

 smooth, not distinctly tuberculate as in P. scaber. The flagellum of the 

 second antennas has the first joint somewhat shorter than the second. 

 The apical segment of the body is flat above and subacutely pointed at 

 the tip. This species, like P. ratzeburgii, belongs to a section of the 

 genus in which all the pleopods have the opercular branch provided with 

 trachea? (or pseudo-trachea?), modified that is to say for aerial respira- 

 tion. In the other species above mentioned it is only the first two pairs 

 of pleopods that are thus modified. In the male of P. rathkei the seventh 

 pair of legs have the antepenultimate joint dilated near the base, a peculi- 

 arity to which attention has been called by Professor G. O. Sars. 1 The 

 cosmopolitan species, Metoponorthus pruinosus (Brandt), taken by Mr. Webb 

 at Langley and Eton Wick, agrees much in general shape with Pbiloscia 

 muscorum, but in other respects more with Porcellio. It has the first two 

 pairs of pleopods tracheate ; the frontal margin is straight. The second 

 joint of the antennary flagellum is much shorter than the first. The 

 apical segment of the body is short, acutely triangular. The surface is 

 finely granular and in colour brown. To the same family belongs the 



* Crustacea oj Norway, ' Isopoda," ii. 1 80. 

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