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Isopods under consideration, their true nature, when present, is often- 

 times obscured, yet, by a little care in the examination, it may be at 

 once seen, though somewhat disguised. 



Their presence in the cephalo-thoracic rings seems to be constant in 

 all the genera I have examined, or of which detailed accounts are ex- 

 tant ; though sometimes, as in Ligidium, the suture which divides them 

 from the edge of the true epimerals is so faintly marked as not to be ap- 

 preciable ; hence I suspect that Lereboullet laboured under an error in 

 supposing them absent in Ligidium Persooni, for an examination of his 

 own figures of the articulation of the ambulatory legs shows that they 

 must be pre ent, from the position of the articulation of the first joint, 

 which arisess from beneath a ledge which evidently is the coxae of the 

 limb : it is hazardous to speak positively on this point without an exa- 

 mination of specimens, but in Armadillium, Ligia, Philoscia, Philougria, 

 Porcellio, and Oniscus, I find them well marked, and they are figured 

 or recorded in Itea, Titanethes, Tylus, and several other genera. In 

 the abdominal segments there may be some question of their presence, 

 but what are usually called the posterior angles of the rings a very lit- 

 tle examination shows really to be these coxae. This is remarkably 

 well seen in Ligia, and, judging from Dana's figures in Tylus above 

 all, where they appear to be regularly articulated to the rings in the 

 eight, i. e. the first abdominal segment. Dana appears to have over- 

 looked this character altogether ; there is some great confusion in his 

 figures : many of the species certainly are not belonging to the genera 

 to which he has referred them, — I may instance Oniscus nigrescens, 0, 

 maculatuSy and 0. puhescens, which are most certainly not Oniscus, but 

 most probably Philoscia judging from the figures of the false feet. 



An additional e-vidence of the true nature of these posterior angles is 

 afforded by the mode of articulation of the posterior false feet, which is, 

 in some of the genera, by means of a regular ball and socket joint. 



Regarding their development in the abdominal segment (i. e. the 

 pleon and telson of Spence Bate), we find the following types: — 



1 . Coxae present in both cephalo-thoracic and abdominal segments, 

 and of nearly equal proportional development. This includes Ligia, 

 Tylus. 



2. Coxae present in first five abdominal rings only, two types. 



{a) Narrow, so that abdomen is much narrower than last cephalo- 

 thoracic ring. The coxae of first and second abdominal segments con- 

 cealed beneath last cephalo-thoracic segments. The third ring of the 



abdomen much wider than the second ; this reaches its limits in 



Titanethes. This type includes Ligidium, Titanethes, Philoscia, and 

 perhaps Dana's new genus, Scyphax. 



{h) Coxae present as before, but extremely narrow, and not concealed 

 beneath cephalo-thoracic rings. This includes Itea (?), Philougria, and 

 probably Trichoniscus, and Deto. 



3. Coxae present in third, fourth, and fifth segments. In the first 

 and second segments the coxae, if developed, are so linear as not to be 

 recognisable. This includes Porcellio, Oniscus, and probably Platyar- 



