254 COLE 
correlated with these, giving some justification for the groupings, 
but it is not at all improbable that widely separated forms are in 
this way often put together; conversely, specimens of the same 
species but of different ages have sometimes been placed even in 
different families.' Like my predecessors, however, for want of 
a better standard, I have retained those groupings which seemed 
most convenient. 
In the matter of the terminology of parts I have, with a few 
exceptions, followed that given by Meinert (’99) in the ‘ Pycno- 
gonida of the Danish Ingolf-Expedition,’ which in turn differs 
little from that used by Sars (’91, and previous papers). In using 
this system rather than the more non-committal nomenclature of 
Dohrn, I have been influenced by two considerations. In the first 
place, these names, or names much like them, have been on the 
whole more generally employed in works on Pycnogonida. Sec- 
ondly, the Pycnogonida form such a highly specialized and well 
differentiated group that terms similar to those used for other 
classes of Arthropoda can be employed without necessarily im- 
plying that the parts so designated are homologous, but merely 
analogous in position, shape, or use. Furthermore, the tendency 
of recent writers has been to use special names for parts, rather 
than more general appellations, and it is of the utmost importance 
that some system should be uniformly established. 
In the following pages the word ‘body’ is used as a general 
term to include the proboscis, caudal segment, and lateral processes, 
while ‘trunk’ has for convenience been restricted to only the main 
portion of the body, the proboscis, caudal segment, and lateral 
processes being excluded. Instead of ‘ovigerous leg’ the word 
‘oviger’ has been employed, and simply ‘leg’ is made to take 
the place of the cumbersome phrase ‘ambulatory leg,’ as there is 
no danger of confusion. When the tarsal joints and the claw are 
spoken of as a whole, that portion of the leg is called the ‘ foot’; 
and when the ventral margin of the second tarsal joint is differen- 
tiated, the basal expansion is spoken of as the ‘heel,’ and the 
1Thus Wilson (’80), before it was recognized that Ache/ia included merely the adults 
of those forms placed in the genus Ammothea, put Ammothea in the family Nymphonide, 
while Achelia was classed along with Zanysty/um in a family which he called the 
Achelidz, 
