233 



tome shows distinctly through the cast. The labrum [hypostome] is im- 

 perfect, but exhibits a strong marginal groove, and two small lateral 

 furrows. 



The body rings have the axis as broad as the sides, and moderately 

 convex. The pleurae are flat as far as the fulcrum, truncate at their ends, 

 and have but a slight groove, which reaches two-thirds of the length. 

 The fulcrum is at one-third in front, and less than half way out in the 

 middle pleurse. 



The caudal axis extends three-fourths down the smooth tail, very in- 

 distinctly marked above, but in some specimens crossed by several faint 

 rings, and is always prominent at the tip." 



The Cape Breton form, by its hypostome, it is cleaaly within Calla- Other i 

 way's genus asaphellus. Allowing for the distortion of the type species, Canadian^ 

 figured by Salter, it is quite as large. variety differs. 



Certain features, not mentioned by Salter, are characteristic of the 

 Cape Breton form. The glabella is somewhat ridged along the axial 

 line, and its margins more distinct. About one-fifth of the length of 

 the head shield from the back there is a slight but distant prominence 

 (scarcely a tubercle) on the axial line ; a fairly marked tubercle is also 

 found on the median line of the axis of the pygidium, at the back of the 

 first ring, and faint traces of similar prominences on succeeding rings. 



The genal spines are not as short as Salter's description indicates for 

 the Welsh form for the points are opposite the fourth segment of the 

 thorax ; the length of the movable cheek and spine behind the facial 

 suture, is just equal in length to the part of the latter behind the eye- 

 lobe. 



The eyelobes are variable in position ; in the type figured they are just 

 half way between the front and back of the shield ; in examples of the 

 narrow form they are, proportionately, further back ; and in both forms 

 the width of the middle piece in front is considerably less than at the 

 eyelobes. 



In the broad form, the headshield, thorax and pygidiuin are each of 

 about equal length ; others have the pygidium shorter than the thorax 

 by the width of one joint. In the narrow form examples occur in which 

 the pygidium is longer than the thorax. The pygidium has more numer- 

 ous somites than A. Homfrayi as figured by Salter.* From A. ajfinis 

 McCoy (ibid) it differs in having the middle piece narrower in front, and 

 the glabella and axis of the pygidium more markedly elevated. 



Young individuals have the pygidium proportionately shorterand wider; 

 one of about 15 mm. in length has a pygidium equal in length to only six 



