34) .BRITISH FOSSILS. 



The resemblances of Pterygotus to the Diastylidce do not extend 

 to the most important and characteristic features of its organization, 

 and even were we to combine together into one form, all the 

 analogous peculiarities which have been noted in these, in Stoma- 

 poda, in Schizopoda, and in larval Podophthalmia, we should not 

 get a sufficiently near approximation to Pterygotus to justify 

 the arrangement of the extinct genus in either of the orders of 

 the higher Crustacea. As I hinted above, however, a stronger 

 case might be made out for the Copepoda. Combine the body 

 of Sapphirina with the eyes and antennse of Corycceus, the man- 

 dibles and maxillae of Calanus, the epistoma and metastoma of 

 Pontella, and the total number of appendages of a copepod larva, 

 and something marvellously like a Pterygotus would be produced. 

 But such an animal would not be a Pterygotus, and even if it 

 were, it would differ so widely from any of the known Copepoda, 

 that its association with the members of that order would be a step 

 of very questionable propriety. Confining the argument to known 

 and existing Copepoda, the differences between them and Ptery- 

 gotus are sufficiently striking. 



No Copepod has truly chelate antennse or antennules, and none 

 present any approximation to the remarkable teeth with which the 

 chelse of Pterygotus are beset. All known Copepods have large 

 thoracic appendages ; no trace of such organs has yet been discovered 

 in Pterygotus. 



No Copepod, so far as I know, presents so great a number as 

 twelve free segments behind the carapace. 



No Copepod has its appendages reduced to so few as three or four 

 pairs, nor, in any, is one pair of the post-oral cephalic appendages 

 converted into the chief organ of locomotion. 



The Pcecilopoda (Plate XVI. fig. 13) are I believe the only Crus- 

 tacea which possess antennary organs like those of Pterygotus, and like 

 them, have the gnathites converted into locomotive organs, want the 

 appendages to the sixth abdominal somite, and present on some parts 

 of the body a remotely similar sculpture. In this order, however, 

 we find but a small labrum, a rudimentary metastoma, a very 

 differently constructed body, and a large number of appendages, both 

 thoracic and abdominal, characters which effectually preclude the 

 association of the extinct Crustacea under discussion with this 

 type.* 



* If the abdominal somites of the Carboniferous Bellinurus, &c. were really free, they 

 would present a certain approximation to the Pteryyoti. Indeed, the evidence that these 

 Carboniferous Crustacea were true Pacilopoda is, to my mind, anything but conclusive. 



