Gatiy Marine Laboratory, St. Andrews. 29 



The first row of hooks is on the fifth segment, the first 

 two elevations being devoid of them. On the fifth the row 

 is at the posterior part of the segment at some distance 

 ventrally from the setigerous process. They increase a 

 little in length after the first, and remain nearly the same 

 for a considerable distance, gradually, however, becoming 

 elevated so that about the twenty-fifth prominent unci- 

 nigerous processes are formed, and posteriorly they stand 

 out like the "feet^^ of caterpillars. Toward the tip of the 

 tail they diminish on the narrow segments, and incline 

 ventrally so that those of opposite sides approach, and they 

 cease at the last segment. In an example from St. Andrews 

 the uncinigerous processes are irregular posteriorly, being 

 crowded on one side and scantily distributed — even with 

 blanks — on the other, probably from injury. The hooks 

 are arranged in a single row throughout and are smaller 

 than those of Lanice conchilega, but more numerous — no less 

 than one hundred and thirty-seven occurring in a row 

 anteriorly, but posteriorly the number diminishes. Each 

 hook in lateral view presents a single tooth above the great 

 fang, though occasionally a minute third is visible. The 

 posterior outline is short and has a dimple, whilst the base 

 is elongated and convex inferiorly. The nnterior outline 

 (below the great fang) is smooth and often slightly convex, 

 and merges into the prow (anterior part of the base), which 

 is prolonged as a stout process with a slightly dilated tip, 

 so as to resemble a stud. The occasional occurrence of a 

 second tooth aliove the great fang brings the Heterophenacia 

 renouardi of Marion"^, from Marseilles, nearer this species. 



Thelepus triserialis, Grube, the seventeenth form, is a 

 southern annelid, in which the cephalic collar and the arrange- 

 ment of the parts of the anterior end are similar to those 

 of the foregoing species, but no pigment-specks remained in 

 the preparations behind the collar, though in life they were 

 present. 



A distinction, however, immediately appears in the bran- 

 chial region, the surface of which is more extensive, the 

 filaments more numerous and more slender. Moreover, thev 

 arise from three segments, viz., the second, third, and 

 fourth. The first and largest forms a transversely elongated 

 row of filaments on segment 2, its outer edge passing 

 ventrally considerably below the first bristle-tnft behind it. 

 The second springs from the dorsum of the third segment 



* Eevue des Sc. iiat. t. iv., March 1876. 



