SCOTTISH TARDTGRADA, COLLECTED BY THE LAKE SURVEY. 665 



majority of the species of Macrobiotus, viz. the claws of the oberhduseri type. 

 Though there is reason to believe that the genus Macrobiotus contains many forms 

 having this type of claw, few such species have yet been described. 



The species of Diphascon need, therefore, only be compared with M. oberhduseri, 

 and species (if any) closely related to it. Those having the narrow pharynx are far 

 removed from any known Macrobiotus, and of the other species only one (D. oculatum) 

 has the pharynx of the oberhduseri type. That species is sufficiently distinguished 

 from M. oberhduseri by several characters— the lack of the brown pigment, the teeth of 

 quite different form, etc. ; the other species are quite distinct in the various details of 

 the pharynx, always associated with oberhduseri claws, even if the distinction of Macro- 

 biotus and Diphascon breaks down. 



For convenience, an artificial subdivision of the genus may be made into — A, pharynx 

 narrow, and B, pharynx round or very shortly oval. 



D. scoticum, Murray (7). (Plate III. fig. 19.) 



The pharynx has the same number of rods as Richters' D. spitzbergense (16), but 

 according to his figure in the " Fauna Arctica " the arrangement is different. He shows 

 the middle narrow rod as the longest, whereas our species has the last narrow rod 

 longest. A more important distinction is the narrow gullet of D. scoticum. 



D. alpinum, Murray (8). (Plate III. fig. 15.) 



The pharynx is intermediate between the round and elongate types, but may be 

 classed with the latter, as it is lj times as long as broad, or slightly longer than that. 



D. bullatum, Murray (7). (Plate III. fig. 21.) 

 The blunt tubercles recall M. tuberculatus, Plate, but there is no other resemblance. 



D. oculatum, Murray (10). (Plate III. fig. 16.) 

 Only known as a moss-dweller till recently discovered in Loch Ness. 



D. angustatum, Murray (6). 

 A simplex form has been found near Edinburgh and at Killin. 



MlLNESIUM. 



Within this genus no variation from the typical structure has been observed of 

 specific value, and I agree with Professor Richters in uniting the two described species. 

 The only variation which I have noticed is in the number of points to the shorter claws. 

 In some districts there appear to be constantly three points to these claws. In Scotland 

 they are variable, and we may find from one to three points, not only in different indi- 

 viduals from one district, but in one individual we may find all three conditions. The 



TRANS. ROY. SOC. EDIN., VOL. XLV. PART III. (NO. 24). 94 



