2 DR J. STEPHENSON ON 
and even more strikingly, it is brought out by comparisons with the descriptions of 
those who have worked in other localities. 
The authors whose works | have used for the purpose of comparison are MacInTosH 
(10), Joupin (7, 8), and Burezr (3, 5). Maclwrosn’s monograph (1873), with its 
valuable coloured plates, represents the chief attempt at an exhaustive account of the 
Nemertine fauna of Great Britain; Jousrn’s works (1890-1894), though without the 
same wealth of illustration, represent a similar undertaking for the coasts of France ; 
BUrGEr’s great monograph (1895) describes in detail the rich Nemertine fauna of Naples, 
with the aid of a beautiful series of plates, and more recently (1904) the same author 
has given in the Zierreich a general systematic account of the whole class. 
It would, of course, have been better if a larger number of authors could have been 
used for purposes of comparison, and especially if the original descriptions of the several 
species could have been utilised for this purpose; but my recent stay in England, 
and, with it, my access to zoological literature, was unfortunately of short duration. I 
believe, nevertheless, that, though thus incomplete, the comparisons I have been able to 
make between the various species, as met with by myself and by previous writers 
respectively, are not without value and interest. 
The variability of Nemertines as a class has long been known as regards colour, 
and in specific diagnoses the colour, though recognised as one of the principal points 
requiring description, is usually stated in wide terms. 
It seems to me, however, that not only colour, but also other characters commonly 
used for purposes of specific distinction, are variable in a high degree. Thus this appears 
to be the case with regard to (a) the shape of the head (compare below, under Lineus 
longissimus, L. ruber, Prostoma candidum) ; (b) the degree in which the head is marked 
off from the body (Lineus longissimus); (c) the length of the specimens (the Millport 
examples of Prostoma candidum and Emplectonema neesvi as compared with MacInrosu’s 
specimens from the East Coast); (d@) the number and arrangement of the eyes (see the 
comparison of the several authors’ descriptions of Lineus longissimus, Amphiporus 
pulcher, and Emplectonema gracile given below, and compare the Millport specimens 
of Amphiporus lactifloreus and also, as regards size of eyes, Prostoma candidum with 
Bireer’s descriptions) ; (e) the cephalic grooves (compare the descriptions of Amphi- 
porus lactifloreus and A. pulcher here given with those of Jousin); (f) the arrangement 
of the musculature (Millport and Naples specimens of Tubulanus annulatus). 
Two variations remain, which seem to demand more than mere mention. The first 
of these concerns (g) the shape of the basis of the stylet. This feature one would 
naturally be inclined to look on as a definite morphological character, capable, if any- 
thing were so, of affording a criterion of specific distinction. Thus Jousrn (9) writes 
concerning it: “ I] peut-étre plus ou moins long, ¢troit ou renflé, pourvu d’ailerons 
latéraux ou presque carré; tous les caractéres sont utilisés dans la détermination des 
especes.” The author who most often describes this structure in species possessing it is 
Bureer, and it is somewhat surprising to find that in most cases (Amphiporus lacti- 
