62 Description of Genera and Species. 



proportionately in their rostra than the females. The integuments are very thin, smooth, 

 and unornamented beyond the usual band bordering the thickened margins and 

 strengthening keels of the web-like organs and the rostrum. The test, which is chitinous, 

 is often filled in with radiating calcareous plates which at times destroy the texture. 



The trunk, including the rostrum, makes up about one-third the length of the 

 body. The carapace, seen sideways, as it is usually preserved, is roughly triangular, being 

 much wider behind and produced into a sharp triangular rostrum in front, surmounted 

 bj' a sharp keel which is continued inwards on to the gastric region of the carapace. 

 There is a small orbital spine and a distinct antennal spine at the antero-lateral angle. 

 There is a slightly-marked cervical fold, but it is often masked by the collapsing of the 

 hodj of the mandible ; the lateral wings or lappets of the carapace are bordered by a 

 narrow double band which is continued round the well-rounded postero-lateral angles, 

 and deeply re-entrant posterior margin. The carapace is only attached to the first few 

 segments, and loosely covers the others, so that in most of the fossils it is usually found 

 somewhat displaced relatively to those segments and their attached organs (figs. 2-4), 

 but is not so much so as in the case of the fossil Lophogastrids and the long-tailed 

 Squillid-like forms already described. The deep emargination behind leaves the dorsal 

 part of the last trunk segment bare, while at the same time the side wings lap well back 

 on to the epimera of the first tail segment (figs. 3, 4). They also appear to have extended 

 rather further down the sides than in the modern pelagic foi-ms of Euphausiidse, The 

 trunk segments, with perhaps the exception of the last, are soldered together, the latter 

 alone forming a complete ring, all the others being deficient dorsally where covered by 

 tlie carapace, while the sternal parts are strongly developed, so that the segments appear 

 sideways as a series of wedges set at a considerable angle to the axis of the body, the 

 angle becoming more and more acute in the more anteriorly-placed segments (fig. 1). 

 The tail, which is made up of the usual six segments and telson, is slightly fusiform, 

 attaining its greatest depth about the second or third segment and tapering gently back- 

 wards to the base of the tail fan, each segment becoming in succession slightly longer 

 than its predecessor, there being a sudden accession in the sixth segment, which is nearly 

 double the length of the preceding one. As the third segment is considerably longer 

 measured along the mid-line of the back than at the fulcra, the tail, when extended, has 

 a natural arch at the third segment (figs. 1, 2). All the tail segments are well facetted 

 and pivotted for rolling, and supplied with epimera which are deep and all overlap each 

 other in regular backward order. Those of the first segment are considerably shorter 

 than those of the second, and are overlapped in front by the hind lappets of the carapace ; 

 those of the second are larger and deeper than the succeeding ones, and are not so much 



