264 PROCEEDINGS OF SOCIETIES. 



An additional evidence 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 coxa? 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. 



(b) 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- 

 thus. Scyphax also, judging from the figures, belongs to here ; it may, 

 however, form a distinct type, as the coxae of the second appears to be 

 developed. The animal figured by Dana as the young of this genus can 

 scarcely be so, unless it be an exception to all the rules which regulate 

 the form of the young in this family. He has himself proposed to call 

 it Actaecia. 



4. Coxae present in second, third, fourth, and fifth rings, the sixth 

 reduced to its minimum : Armadillo, Sphaerillo. 



II. — The Form of the JSead. 



We shall next examine the arrangement of the various parts of the 

 cephalic segment, or, as I have called it, the head ; these are of minor 

 importance, but still assist much in classification. It will be necessary 

 to examine the native genera in detail. 



Ligia, Plate XX., Figs. 7 to 10. 

 "When the head is looked down on from the front, we remark an- 

 teriorly just beneath but not attaining to the frontal line of the head, 

 a broad plate extending over the entire forehead, and divided transversely 

 by a raised ridge ; its superior margin also marked by a raised ridge. 

 This superior ridge passes off on each side beneath the eyes, forming at 

 least a third of the inferior border of the orbit. The external angle of 

 the orbit, however, is formed, not by this, but by the cephalic ring con- 

 tinued forwards from behind, and terminating as a rounded knob just 

 above the external antennae ; these arise in the angle between the in- 

 ferior border of the frontal plate and the projecting lobes. The inferior 

 border of the frontal plate is formed of two curves, convex upwards, one 

 over the origin of each external antennae ; the angle of their junction is 



