46 BRITISH FOSSILS. 



convex central portions. The first segment is much more rounded 

 off at its hinder angles c than the remainder, and the space thus 

 left filled by a projecting process of the second segment (see also 

 Plate IV.) There is a similar but smaller process to the first joint, 

 at least in the var. plicatissimus, fig. 1 6, and it is probably so 

 in all species. 



The sculpture in the body rings, fig. 13 a, extends over less than 

 half their surface. The plicae are open forwards, very small, almost 

 linear on the front margin (the extreme margin of all the segments 

 is rounded off and smooth) and the remainder are less than semi- 

 circles or they are subangular (more than 90). On each side at 6 

 they are not as wide. A transverse impressed line separates the 

 anterior sculptured half from the posteripr smooth portion, but this 

 is not always present. No crenate edge has yet been observed. 



Appendages, Plate XV. fig. 2. 



On a specimen much distorted, and from which the swimming 

 foot, Plate I. fig. 13*, is taken, the following organs maybe detected 

 by careful examination : 



Epistoma, /, reflected from the under side. 



Antennae, 6, b'. 



Great post-oral plate or metastoma, g. 



Two endognaths, c, c, with palpi x. 



Endognath (mandible or maxilla) of the opposite side, c". 



A separate jointed palpus. 



Ectognath (swimming foot), e, attached to the carapace. 



First body joint. 



/. The large epistomian plate resembles much in shape that seen 

 in Plate I. fig. 1 a, which is similarly displaced. We only see a 

 portion of it, the termination being broken off, but it appears to have 

 been semicircular and semioval, more than three-fourths the width 

 of the carapace, and covered with minute prominent plicas. Near 

 its base, but not attached, are remains of a single antenna, b. 



b, b', Antenna. Only the general form can be made out; it is 

 thick in proportion to the size of the specimen, and consists of 

 apparently only three joints, the lower one broken (6), the frag- 

 ment three times as long as wide ; the second (&'), crossed by a line, 

 which is probably a fracture, appears to be a long single joint, five 

 times as wide as long, its articulation with the neighbouring joints 

 being marked by small irregular crenulations. The penultimate 

 joint or fixed finger b" is much crushed, it seems to be contracted 



