THE NEMERTINES OF MILLPORT AND ITS VICINITY. 3 
floreus, A. pulcher, Prostoma candidum, Oerstedia dorsalis) the Millport specimens 
show a wide divergence from the Naples forms. It is curious, too, that one particular 
difference repeats itself in all these cases—the Naples forms show a marked constric- 
tion about the middle of the basis, which is scarcely to be observed at all in the same 
species as found at Millport. In the case of Amphiporus lactifloreus the shape varies 
even among the Millport specimens. 
Attention may here be called to the fact that; OxnER (12) has also found the shape 
of the basis to be variable in Prosorochmus delagei, a new species described by him. 
He says : “ La forme et les dimensions du socle peuvent subir de nombreuses variations. 
Cette variation est un trait caracteristique pour P. delagei.” The figure shows that 
the basis may either present a constriction or not, that its posterior end may be either 
wider or narrower than the anterior end, and that its size may vary, both relatively to 
the size of the stylet, and also absolutely. He, however, supposes, as we have seen, that 
this variability is a special feature of this particular form. 
The fact that BUrceEr in different works gives two different shapes for the basis of 
the stylet in Prostoma flavidum is presumably also to be explained by the variability 
of this structure. In the Naples monograph, the figure shows it as somewhat dumbbell- 
shaped—that is, with rounded ends of equal size, and a constriction in the middle ; 
in the Tverreich, however, it is described as “Der kegelformige, kaum in der mitte 
eingeschniirte Sockel.” 
Lastly, (1) the number of proboscis nerves furnishes an example of another definite 
morphological character which might have been supposed to be constant and capable 
of furnishing a criterion of specific distinction. Yet Amphiporus pulcher is stated by 
Burcer in the Zierreich to possess ten proboscis nerves, while the Millport specimens 
examined for this character showed twelve. 
The importance of a recognition of the variability of the above-mentioned characters 
lies in the fact that they are among those which are most frequently used for purposes 
of diagnosis. With regard to the shape of the head, for example, the details of which 
are used in many genera as specific distinctions, and in some cases take the chief, or at 
least a leading part, among the criteria of diagnosis, one constantly meets, combined in 
various ways, such expressions as spoon-shaped, lancet-shaped, egg-shaped ; marked off, or 
not marked off from the body; wider than, shghtly wider than, or not wider than the body. 
Consider for a moment such specific diagnoses as these (Zverreich)—(i.) Prostoma 
vermicularis (Quatr.): ‘‘ Vorderende verbreitert, Hinterende etwas verjiingt. Kopf 
spatelformig, nicht vom Rumpf abgesetzt. Mit 4 kleinen Augen, die im Rechteck 
stehen. L. 12-15, Br. kaum 1 mm.” * 
(ii.) Prostoma flavidum (Ehrbg.): ‘Kopf vorn abgerundet, spatelformig, nicht 
vom Rumpf abgesetzt. Rosenfarben, Seitenriénder durchscheinend. Mit 4 einfachen, 
sehr kleinen Augen, die im Rechteck stehen. Angriffsstilett ein wenig linger als der 
* P. vermicularis is divided, certainly, into three sub-species, which are distinguished among themselves by various 
markings or the absence of them. The above, however, constitutes the whole of the specific diagnosis, 
