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. 1 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 



1 Thus Wilson ('80), before it was recognized that Achelia included merely the adults 

 of those forms placed in the genus Ammothea, put Ammothea in the family Nymphonidae, 

 while Achelia was classed along with Tanystylum in a family which he called the 

 Achelidse. 



