20 



downward, and at their fulcral points they are slightly 

 bent backwards. The pygidium is long and acutely tri- 

 angular, terminating in an extended niucro ; its axis ta- 

 pering posteriorly to its acute termination, which has 

 from 28 to 30 distinct side notches, the centre is smooth 

 and has 7 ]>rominent tubercles, 4 articulations interven- 

 ing between two tubercles ; 8 pleurte on each side of 

 the axis, gradually decrease in size as they approach 

 the termination of the pygidium ; the anterior pleurae 

 curve backward, and they are separated by deep fur- 

 rows, and« distinct tubercle is placed upon the upper 

 and inner part of each pleurae, near the dorsal furrows. 



According to Nieszkowski, between the 1st, 2nd and 

 3rd tubercles of the axis of the pygidium, 2 notches 

 appear ; between the 3rd and 4th, 4 notches ; between 

 the 4th and 5th, 4 to 5 notches appear, and between the 

 5th and 6th, 5 to 6 notches. 



Wahlenburg represents on pi. ii, tig. 1, a pygidium 

 with 7 tubercles and 28 notches on the axis, and 8 seg- 

 ments; Angelin's copy of the same, figured on pi, iv. fig. 

 4, has 8 tubercles and 26 notches on the axis, with 8 

 pleurae. Both these specimens are from Gothland. Dal- 

 man's representations of the pygidium on pi. ii, fig. 2a 

 and 2b, have 5 and 6 tuburcles on the axis, and 7 pleurae ; 

 Corda, on pi. v, fig. 55, represents a copy with 6 tubercles 

 and 22 notches on the axis, and 7 pleurae : Nieszkowski 

 figures a specimen from Oesel, with 6 to 7 tubercles and 

 25 to 28 notches on the axis, with 8 pleurae. 



Geological localities — Upper Silurian : Dudley, Gott- 

 land, etc. 



Lower Silurian : Bala Rocks, Pwllheli, Carnarvon- 

 shire. 



