22 HINDE, ANNELID REMAINS FROM SILURIAN OF GOTLAND. 



Jaws triangulär in outline, consisting of a basal fiange 

 with an obliquc ridge, on the summit of which are the den- 

 ticles. The right and left jaw plates differ from each other. 

 In the left forms, the oblique tooth-bearing ridge springs from 

 the outer lateral margin of the basal plate, which is only ex- 

 posed on the inner side of the ridge. This basal plate is con- 

 cave immediately beneath the oblique ridge, an<l has a stout 

 upward projecting shank in the middle of its length, and be- 

 low this, the plate rapidly contracts to the posterior end. The 

 oblique dental ridge is curved in front and then becomes nearly 

 straight, it has a series of 15 to 18 denticles, ef which the 

 anterior two or three are more prominent and curve inwards, 

 those following are rounded or conical and directed back- 

 wards. The anterior denticles are frequently worn down so 

 that they appear as mere hollow stumps. 



In the right jaw plate the basal flange is wider, nearly 

 flat, and extends on both sides of the toothed ridge. The 

 central portion of the inner margin has a thickened promi- 

 nence which, however, does not project into a shank as in 

 the left jaw plate. The dental ridge is nearly vertical to the 

 basal flange, and extends longitudinally down it. The cha- 

 racter and number of the denticles correspond with those of 

 the left jaw plate. The under surface of both right and left 

 jaws has the anterior portion arched över and gently con- 

 vex, below this to the posterior extremity the jaw is hollow, 

 and open, so that even the hollow bases of the denticles can 

 be distinguished. In the left jaw plate the under surface of 

 the shank also exhibits a concavity. These jaws are from 1,7 

 to 2,1 mm. in length, and about 0,7 mm. in extreme width. 

 They are very abundant. 



Though these right and left jaws occur quite detached from 

 each other, I regard them as belonging to the same species from 

 the fact of their correspondence in dimensions and in the cha- 

 racter of the denticles Avhilst the differenccs in the form of the 

 basal flange and the position on it of the dental ridge, are ^ 

 limited to the right and left forms respectively. The perfect 

 preservation of these Gotland specimens has enabled me to 

 determine, that in some of the Canadian forms but partially 

 exposed on the rock surface, the toothed ridge was sup- 

 ported on a basal flange; whereas I had regarded it as 

 the edge of the jaw plate itself, and thus placed these forms 



