108 



BRITISH FOSSIL CRUSTACEA. 



of the median line, each composed of from three to four tubercles arranged in a line, with 

 their blunt points directed backwards. The sides of the anterior segments are rounded 

 and the hinder border but slightly incurved, like the posterior border of the head. A line 

 is usually seen crossing each segment parallel with its anterior border, and indicating 

 the portion of each body-ring inserted beneath that of the preceding segment. At first 

 sight there does not appear to be any trace of the squamate ornamentation, covering the 

 surface of the segments, so characteristic of other members of this sub-order ; but, although 



Fig. 30. — Plicae, greatly magnified, from an abdominal ring in Slimonia acuminata, Salter, sp. 



rarely seen, it may occasionally be detected upon the anterior border of the somites; the 

 plicse are, however, very minute, and not at all conspicuous as in Pterygotus anglicus. 



The foregoing measurements do not represent by any means the largest-sized body 

 known. A detached body, in which the first six somites (thoracic) are conjoined, pre- 

 served in the British Museum, gives the following measurements : — 





No. 



Breadth. 



Length. 



1st Segment (8) 



H 



inches 



by 1 inch 



2nd 



(9) 



8* 



j> 



IJL 



)> 1 4 33 



3rd 



(10) 



8f 



j> 



11 

 33 - 1 2 " 



4th 



(ID 



8 



33 



11 

 33 -*- 2 " 



5th 



(12) 



n 



33 



IJL 



33 ■*■ 4 jj 



6th 



(13) 



6 



33 



IJL 



33 - L 4 33 



Abdominal Segments. — These commence with the fourteenth somite, and, in the 

 specimen figured in PL XVII, measure as follows : — 





No. 



Breadth. 



Length. 



7th Segment (14) 1 



H 



inches 



by 1 inch 



8th 



(15) 



01 



~4 





li 



33 x 2 33 



9th 



(16) 



2 





33 J- 2 33 



10th 



(17) 



2 





1^ 



33 x 4 33 



11th 



(18) 



If 





2 



3 3 - v 3 3 



12th 



(19) 



If 





21 



33 ^i 33 



The sides of these posterior segments are nearly straight ; they have no keel-markings, 

 as is the case with the thoracic segments, nor are their borders produced at all. 



1 See foot-note l , ante, page 107. 



