184 Proceedings of the Eoyal Physical Society. 



longer than the first, and bent back from it at a considerable 

 angle. There is an appearance in the slab in which the 

 fossil occurs as if this antennae extended further, but in such 

 a crushed state that the individual segments are not recog- 

 nisable. Two specimens belonging to this genus have been 

 studied, and from the depressed character of the animal and 

 its having possessed such wide lateral lamellae, they have 

 both been fossilised back up. The following measurements 

 give the proportions of such part as have been preserved, it 

 must be remembered, in a collapsed state : — 



The specimen from which fig. 2 and 2a are taken 

 measures — 



From head to tail, along the curve, 47 mm., the body consisting of about 

 seventy-seven segments, not counting the head. 



Length of head, 3 '5 mm. 



Breadth of anterior portion of head, 2 mm. 



Breadth of posterior portion of h ead, 2 '5 mm. 



Breadth of body, including the lateral lamellse across the twentieth seg- 

 ment from head, 5 '25 mm. 



Breadth of nineteeth segment, which bears no lamellae, 275 mm. 



Breadth of body at about the twentieth segment from tail end, 2 mm. 



Breadth of body close to tail, 1 mm. 



Length of leg attached to twentieth segment from tail, 3 mm. 



Breadth of above leg at base, "5 mm. , increasing slightly to end of second 

 joint. 



Length of leg attached to above segment, which measures 1 mm. across 

 close to tail end, 3*5 mm. The legs, therefore, appear to increase in 

 length backwards. 



In the fragmentary specimen from which fig. 2h is taken, 

 there is scarcely any appreciable taper, the inference being 

 that the middle portion of the animal only is preserved to us. 

 It measures 50 mm., and shows sixty-two segments. The 

 average breadth of segments across the lateral lamellae is 6 

 mm., the smaller intermediate segments only measuring 3 

 mm. It is easily seen that this latter fossil must represent 

 the remains of a much larger individual than that shown in 

 fig. 2. 



This species is called after Walter MacMcol, Esq.', the 

 finder of the specimen from which fig. 2 is taken, who has 

 done so much towards unearthing the fauna of the Lower 

 Old Red Sandstone of Forfarshire. 



