British Species of Siphonostoma. 193 



of intermediate length are intermediate in character between 

 the two. 



Specimens of 60-70 millim. in length had 40-45 segments. 

 This does not agree with St. Joseph's statement for 8. diplo- 

 cha'itos, but Bies *, in speaking of this species (Naples 

 specimens) says 40-50 segments, so that there must obvionslj 

 be variation in tliis respect. The gills in these full-grown 

 specimens numbered about 100, the cephalic bristles 200 or 

 more ; but in the structure of notopodiuni and neuropodium 

 they showed less close agreement with St. Joseph's specimens. 

 The notopodiuni bore usually 10-12 long annulated bristles, 

 but in addition there were about 10-13 other short bristles 

 buried in the substance of tlie papilla, and liardly, if at 

 all, visible externally (see PI. IV. fig. 1). The distance of 

 the annuli apart varied from 0"02G millim. to 071 millim. 

 in the cephalic bristles, and from 0'0079 millim. to 023 

 millim. in the other notopodial bristles (see fig. 3). The 

 range of variation in this respect is thus very wide. As to 

 the hooks of the neuropodium, these did not exceed 3 in 

 number (in place of 4-5), and in many instances 1 or 2 only 

 were present ; but it may be noticed that the hooks fall out 

 very readily. The annulation was often indistinct throughout 

 a portion at least of the iiook (see fig. 4), and in no case did I 

 succeed in finding any one hook which displayed all the 

 characters described by St. Joseph. He describes his speci- 

 mens of 8. diplochaitos as having less distinctly recurved 

 hooks than those of 8. ajffinis ; but my specimens showed no 

 such distinction. Embedded in the neuropodial papillte and 

 surrounding the base of the hooks there are, as in 8. affinis, 

 short annulated bristles whose slender tips only project from 

 the surface of the papilla (see fig. 2). In the Millport speci- 

 mens instead of 6 of these there were usually about 13 : of 

 these about 7 actually projected from the papilla; the other 6, 

 though identical in structure, lay entirely within the substance 

 of the papilla (see fig. 2). It seems impossible to doubt the 

 identity of these Millport specimens with 8iphonostoma diplo- 

 chaitos of the Mediterranean ; but they differ especially in the 

 diminished number of ventral hooks and in the presence of 

 small bristles in the notopodial papilla, in addition to the 

 typical immber. 



The small Millport specimens diflfered in several respects 

 from the large. Specimens of 25 millim. in length had 

 34-35 segments, but one of 38 millim. had 43 segments. In 

 specimens of 25-40 millim. the number of cephalic bristles 



* Brit. Assoc. Report, 1891. 

 Ann. & Mag, N. Hist. Ser. 7. Vol. v. 13 



