;58 ^Ir. 11. I. Pocock on the Taxonomy 



the American form that liavo been received, dead and alive, 

 in Enghmd within the hist twenty years, we are very 

 badly oft' for examjiles of this s|)ecies. Any s|)ecimens that 

 anatomical lecturers have to spare would make a welcome 

 addition to the national series. So, too, with the Oriental 

 species. There is probably a great deal yet to be learnt 

 about them ; yet S|)ecimens are usually considered not worth 

 the bringing, or not worth the keeping if brought. Espe- 

 cially is it to be regretted that none of the ' Ciiallenger ' 

 material has found its way into the British Museum. Presu- 

 mably it was dispersed for anatomical purposes, and discarded 

 as useless when done with. 



Part 111. — Generic and Specific Chaiucters. 



Most of the characters here used as a basis for classification 

 are manifest enough. Some have been employed before, but 

 with oidy a specific valuation, and many of the most obvious 

 are figured in Van der Hoeven's classic monograph, though, 

 oddly enough, they are completely ignored in the text. In 

 the specific diagnoses, for example, while great stress is laid 

 upon the relative prominence of the posterior angular prolon- 

 gation of the opisthosoma, the serration and shape of the 

 postanal spine, the form and immber of claspers in the male, 

 yet the structure of the genital operculum and the radical 

 differences that obtain between this ajjpendage in the Ameri- 

 can and the Oriental species, the absence of the spur on the 

 sixth leg in roiundicauda, the absence of the si)ike on the 

 sides of the gill-chamber in poli/phemns, the difference in 

 jjosition ot the anterior spike of the lateral series on the opistiio- 

 soma in the two sets of species — all of which the artist has 

 laithfully poitraycd — are passed over unnoticed in the letter- 

 press. The same omissions are observable in the work of 

 H. Milne-Edwards in 1840 (Hist. Nat. (Jrust. iii. ])p. 547- 

 550). These authors, in fact, like their predecessors, evince 

 only superficial acquaintance with the external structural 

 features of Linmlus or an inappreciation of their value, 

 k^ubstquent writers have for the most part paid attention to 

 the more ijmportant questions relating to tiie affinities of this 

 animal with other Arthropoda, setting aside as uninteresting 

 or well kno-wn the affinities of its species to one another. 



Ihe organ which sup|)lies the basis for the classification 

 given below is the genital operculum. As was long ago 

 pointed out in Claus's ' Lehrbiicli,' this appendage diffi-rs 



