Gatty Marine Laboratory^ St. Andrews. 157 



and a median furrow; whereas ventrally the segment is 

 undivided, each being separated by a deep furrow at the 

 junction in front and behind. In the next region, where 

 branchiae are less, the dorsum has an elevated transverse 

 ridge with a narrow groove and a belt in front and behind. 

 Ventrally a broad ridge with a furrow, and a narrower belt 

 in front and behind, occurs. Still further backward, and 

 where the branchia is represented by a rounded papilla, the 

 dorsum shows an elevated transverse band with a more or 

 less distinct median furrow, an enlargement in the centre of 

 the dorsum anteriorly and one at each side, the intermediate 

 region being marked by transverse lines. On the ventral 

 surface a similar elevated transverse band is present, but the 

 lateral enlargements are indistinct, and though there is an 

 interrupted median band no median enlargement of the 

 transverse band is visible. 



The feet are furnished with branchiae from the second 

 backward, and they are amalgamated with the superior 

 lamella from the 2nd to beyond the 50th. The inter- 

 lamellar notch is distinct. The ventral lamella, at first 

 prominent and rounded, becomes narrower and elongated 

 from above downward on the appearance of the winged 

 hooks. The latter occur in the superior division about the 

 70th bristled foot (Mesnil gives the 65th). The bristles in 

 the upper division in front form two groups, a long upper 

 series and a shorter inferior, all curved, dappled, and finely 

 tapered. At the foot just mentioned (70th) the branchia 

 has lost much of its external frilly, and is again separated 

 inferiorly from the posterior fillet of the upper division 

 of the foot, which rises into a prominent border superiorly. 

 The anterior fillet has disappeared in both divisions, and the 

 fillet from the second ring of the segment runs up behind 

 the posterior fillet at its ventral edge. The bristles in the 

 upper division remain simple, but are more slender than in 

 front. The inferior division carries winged hooks, with the 

 exception of a few bristles superiorly and inferiorly. Tlie 

 cliief changes toward the posterior end are the diminution 

 of the branchia (which at the 125th foot forms a process less 

 than the vertical diameter of the upper fillet), the diminution 

 in the number of the superior bristles (which are in a single 

 fascicle), the abbreviation of the upper border of the long 

 fillet of the ventral division, and the increase and pro- 

 minence of that part of the fillet bearing the bristles 

 and hooks. Finally, the branchia diminishes to a minute 

 rounded papilla, the upper fillet is short and almost semi- 

 circular, whilst a broad gap separates it from the inferior 



