220 J. MURRAY ON PHILODINA MACROSTYLA, EHR., 



constriction marking the limit of the central trunk (this segment 

 I believe to be homologous with Bryce's 4th central segment). 

 In all the descriptions the supposed homologous rows of spines 

 will be indicated by the same numbers, 1 to 6. 



12 Spines. 



Variety. — One of the commonest forms in Scotland, and having 

 the largest number of spines which I have been able to study in 

 the living animal. The spines correspond exactly with those of 

 var. medio-aculeata, except that the anterior median spine is 

 absent. I have not seen the median spines in any Scotch 

 examples, nor has Milne (15). (See Fig. 1.) 



Var. crystallina var. nov. (Figs. 8, 9). Spines twelve, in six 

 pairs, one lateral pair pointing forward, corresponding with those 

 of var. medio-aculeata, but the median spine lacking. Trunk 

 covered with large hemispherical tubercles, which form longi- 

 tudinal rows on the dorsal, and transverse rows on the ventral 

 surface. The plication of the trunk includes the tubercles 

 between the folds, so that they do not appear as prominences 

 in the profile of the body. 



The whole trunk is clean, and free from any secretion, and 

 beautifully hyaline. 



This variety, having real tubercles, might be taken as Gosse's 

 P. tubercidata, but the spines distinguish it. Gosse describes 

 the tubercles as rough, and the colour as dark brown, which 

 makes it highly probable that he had in view examples of 

 P. macrostyla having the trunk coated with deep plates formed 

 of a viscous secretion. 



The var. crystallina is one of the most beautiful of Bdelloids. 

 It recalls Callidina formosa, Murray (16), but in that species 

 the tubercles crown the skinfolds, and thus appear on the 

 profile, while in this they are between the folds, and do not 

 show on the outline. 



This gives ordinarily the appearance of simple wrinkling, but 

 careful study shows that these are really independent tubercles, 

 of extreme uniformity of size and regularity of disposition. 



I have never seen this variety with any trace of the viscous. 



