BRITISH FOSSILS. 77 



The surface of the great basal joint is nearly covered with large 

 plicse or squamse, the convexity of which is outwards over the 

 lower and hinder half, and inwards along the front margin. The 

 other joints are more strongly ornamented, the plicse coarsest on the 

 exterior margin; on the three or four terminal joints they are only 

 obscurely visible except on the margin. 



The margins of at least the two last segments are beautifully 

 crenulated all round, with appressed serratures ; these are largest 

 at the apex and inner edge of the terminal swimming palette. 



Metastoma, Plate VI. fig. 7. The only piece which remains to 

 be described is this large oval plate, deeply notched at the broader 

 anterior extremity, regularly rounded on the sides, and very slightly 

 truncate at the posterior end. These plates are sometimes four 

 inches long and three broad, and are oval, the greatest width being 

 less than half way from the notched end; flat on one side and 

 of but slight convexity on the other, except at a point on the median 

 line about one-third distant from the smaller end, where there is a 

 prominence (probably the point of insertion). They are more 

 covered with sculpture than in the species previously described. 



FIG. 11. 



Packets of eggs or ovisacs (Parka decipiens). No. 1 is from a specimen in the 

 cabinet of Lord Kinnaird. 



(Parka decipiens, Fleming. See Siluria, 2nd ed. chap. 10.) These 

 occur too often with Pterygotus not to be suspected as part of its 



