218 J. MURRAY ON PHILODINA MACROSTYLA, EHR., 



Pritchard (17), etc., have probably only followed Ehrenberg. 

 Miss Glascott (10) claims to have seen an animal answering to* 

 Dujarclin's description; but her own description is evidently of 

 another animal than Ehrenberg's, and in all probability an 

 unnamed species. 



The form with most numerous spines among those which 

 I have seen might, if seen in lateral view, give the impression 

 that the spines are more numerous than they really are, as will 

 be understood by looking at Fig. 16, where only eleven or twelve 

 of the thirteen spines are seen. 



This supposition does not explain Ehrenberg's dorsal view 

 (copied from Pritchard in Pig. 22), which shows closely -set spines 

 all round the lateral margin of the trunk, as many as seven 

 on each side. 



It is rarely that more than two pairs of the backward-pointing 

 spines reach to the lateral margin or project over it. 



Subsequent observers are agreed in identifying as Ehrenberg's 

 P. aculeata an animal possessing a much smaller number of spines, 

 varying from two to thirteen (the largest number I find recorded), 

 symmetrically arranged in pairs, or with an additional median 

 spine in one row. 



All the spines have their points directed backward, except the 

 pair which is furthest from the median line of the body and 

 a little in front of the widest part of the trunk, which point 

 forward. 



This pair is partly or wholly hidden among the skinfolds when 

 the animal is creeping — when fully contracted the tension of the 

 skin forces the points outward, till they stand almost at right 

 angles to the trunk, when they may be supposed to form a 

 deterrent to any animal thinking of having aculeata for dinner. 



Ehrenberg (7) asserts that the spines can be erected at will, 

 and Janson (13) says that they are movable and can be laid 

 against the body. 



No doubt the spines are sometimes erect and sometimes laid 

 close to the body ; but it seems to me that the movement is 

 automatic, and that it is misleading to say that it is done at will. 

 The spines seem to be rigidly joined to the skin, and to assume 



