178 EITSPIO MESNILI. 



tuft. All show traces of wings, and are curved backward. The ventral lamella is also 

 narrow and more or less semicircular, being rounded dorsally and ventrally. The bristles 

 of this division are, as usual, shorter than those in the upper, and show distinct win^s 

 some of the lower bristles presenting a slight dilatation in the winged region (Plate CV 



fig. ii). 



This type of foot rapidly changes, for a flattening of the ventral lamella takes place, 

 and at the fourteenth foot, or sooner, a row of hooks makes its appearance with finely- 

 tapered short bristles, a few of the longer bristles remaining at the ventral edge. The 

 upper division and branchia are unchanged. 



At the twenty-fifth foot (Plate XCVI, fig. lb and Plate CV, fig. 16) the branchia is still 

 longer, though somewhat narrower, but the upper lamella has so greatly diminished that 

 the setigerous process in front of it is now prominent, with its upper series of longer bristles 

 and the lower of shorter, the whole forming a gradually diminishing series from above 

 downward. The wings in these are not distinct. The lower end of the upper lamella 

 is visible as a slight incurvation below the bristles, but there is nothing to indicate the 

 commencement of the inferior lamella except the short bristles and hooks. The bristles 

 (Plate CV, fig. 11a) have distinct wings, are arranged at intervals along the row 

 of hooks, and, besides, a group of three at the ventral edge are peculiarly modified as 

 long curved and apparently flattened forms with a probe-tip. The hooks (Plate CV, 

 fig. 11 b) have straight shafts which slightly increase in diameter as they rise to the 

 backward curve near the tip, but bending backward they again slightly dilate before the 

 constriction at the throat. The strong and sharp main fang comes off nearly at right 

 angles to the axis of the neck, and on the crown in lateral view is a single sharp spike 

 directed forward and obliquely upward. The wings are well developed, the lower edge 

 being attached to the constriction at the end of the shaft just where the distal dilatation is 

 about to commence. 



The branchia is nearly as long at the fiftieth foot, but is narrower, the cuticle and 

 hypoderm having a tendency to form a slight web on the distal half. The upper lamella 

 (Plate XCVI, fig. 7 c) forms a triangular web which has a somewhat abrupt border 

 superiorly, but trends downward with a curve to the foot. The setigerous process forms 

 a similar triangular ridge a little within the foregoing lamella, and carries the long tuft 

 superiorly and the diminishing series beneath. Scarcely a trace of the inferior lamella 

 is visible except the row of hooks and bristles. The three modified bristles conclude 

 the series inferiorly. 



In the posterior feet (Plate XCVI, fig. 7 d) the chief changes are the diminution of 

 the branchia, the prominence of the superior lamella, which has a free ovate-lanceolate 

 tip dorsally, and the elongation of the dorsal bristles, which, however, preserve the same 

 structure. The ventral lamella is distinct, commencing superiorly as a narrow border 

 which curves round the angle to the ventral surface and ceases about the issue of the 

 special group of modified bristles. The hooks are now fewer in number, and issue partly 

 above the ventral angle of the foot and partly below it, the group of specially modified 

 bristles projecting ventralward some distance from the angle. The probe-pointed tip 

 of the latter bristles is often slightly curved. The stout tapering bristles accompanying 

 the hooks are as in front. 



