Description of Genera and Species. 13 



view, the segiueius entering the tail, counting baclcwards from the lirst ov antennule- 

 bearing segment, number from 14 to 20 consecutively. The first segment is very short. 

 There is a sudden increase in the length of the second, and from thence there is a 

 gradual increase of each segment in succession up to and including the anterior part of 

 the sixth, where there is a sudden expansion accompanied by an applanation of the 

 segment for the attachment of the tail fan. To allow of the folding of the tail, all these 

 segments are well facetted on the anterior margins of the back and sides above the 

 pivots which are placed at the bases of the epimera. For the same reason the sternites 

 become very short in the mid-line (fig. 3), M. 4848*^, while the epimera themselves 

 generally overlap each other in turn from before backwards, the anterior margin of 

 each being facetted for the purpose (figs. 3, 4). The outcome of this arrangement is 

 that when the tail is extended it lies much in the same straight line with the trunk, 

 and when flexed it rolls up so that the posterior end (jf the animal makes a complete 

 semicircle. 



The portions of the dorsal plates exposed when the tail is extended are bordered 

 along their anterior margins, and there are sometimes traces of a median longitudinal 

 keel upon the anterior parts of the third and sixth segments l^y the border giving off a 

 backward projection in the mid-line. 



The epimera are well developed (figs. 3, 4) and consist of only one lappet on each 

 side, in this respect differing from those of Gnathophausia and resembling those of 

 Lophogaster and Ceratolepis. They are directed downwards and backwards and end in 

 blunt points. 'I'hose of the first tail segment are, as already stated, overlapped by side 

 lappets of the carapace and are comparatively small. Their posterior margins overlap 

 on to the epimera of the succeeding segments, which are much larger. As alreadj- 

 stated, this order of overlap is maintained up to the sixth tail segment, the epimera at 

 the same time becoming in turn less deep but more bent backwards. The epimera of 

 the sixth segment are not carried so far back as the rest, and only extend to where tlie 

 tail begins to expand. There is no evidence that the epimera on the two sides of this 

 segment are confluent at their base, as in Gnathophausia, but it is difficult to obtain 

 specimens which show the ventral aspect, and owing to the flattening which takes place 

 towards the back end of this segment it seldom becomes fossilised sideways. The evidemie 

 obtainable is rather against the view of their he'uvj, confluent. Tlie telson is elongated 

 and somewiiat heart- or shield-shaped. Viewed from above (figs. 1, 3), it is tumid 

 towards the base and expands slightly for a short distance from the articulation, then 

 it flattens and tapers, at first gradually, and then more rapidly, till at about three- 

 fourths of its length it becomes suddenly constricted, after which it once more expands 



